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Selective embedded growth of GaInAs by low pressure MOVPE
Journal of Crystal Growth 107 (1991) 141—146 North-Holland
141
Selective embedded growth of GaInAs by low pressure MOVPE 0. Kayser, B. Opitz, R. Westphalen Institute of Semiconductor Electronics, Technical University of Aachen, D-5100 Aachen, Fed. Rep. of Germany
U. Niggebrugge, K. Schneider Heinrich-Heriz-Institut Berlin, D-1000 Berlin, Germany
and P. Balk Institute of Semiconductor Electronics, Technical University of Aachen, D-5100 Aac/zen, Fed. Rep. of Germany
The study reported on in this paper is concerned with selective low pressure (20 hPa) MOVPE of GaInAs and GaInAs/InP heterostructures at 940 K in etched recesses in partially masked substrates. Different growth behavior is obtained for the single layers of the ternary and binary/ternary heterostructures. Moreover, the shape of the recesses, which is related to the etching procedure, also affects the cross section of the deposited stripes. Proper choice of the shape of the recesses permits the growth of planar stripes. The feasibility of in-Situ doping of the GaInAs stripes using H 2S or DEZn is demonstrated.
1. Introduction Selective MOVPE (metalorgamc chemical vapor epitaxy) of InP-based compounds is an attractive technique to produce monolithic integration of electronic and optoelectronic devices [1]. One potential application, butt coupling of optical and electrical components (e.g. waveguide/photodiode), requires the regrowth into recessed areas in previously deposited semiconductor films. Moreover, restriction of the deposition process to recesses offers the potential to achieve monolithic integration of electrically insulated films maintaining an overall planar surface. From the application point of view, planar surfaces are necessary for subsequent metallization and lithography steps. Thus, this technology has the potential for the fabrication of a variety of advanced devices and circuits. For butt coupled waveguide/photodiode combinations, the existence of epitaxial contact be0022-0248/91/$03.50 © 1991
—
tween the embedded material and its surroundings is essential, if high optical losses at the heterointerface are to be avoided. The concept to use a regrown structure as a photodiode implies that doping of selectively deposited material is feasible. Post growth doping may render the fabrication of compact devices more difficult. For the deposition of such doped layers, but also for the growth of heterostructures, knowledge of the details of the growth process is essential. Specifically, it will have to be determined if growth takes place only parallel to the bottom of the recesses, or also on the vertical side walls. In general, optical devices require low densities of misfit dislocations of the epitaxial layers in order to avoid non-radiative transitions. This implies lattice matched growth in combination with minimum variation of the composition in the layers. It has already been reported that the composition of selectively grown GaInAs strongly depends on the geometry of the mask [2]. For details
Elsevier Science Publishers B.V. (North-Holland)
142
0. Kayser et a!.
/ Selective embedded growth of GalnAs by low pressure MO VPE
with respect to this question, see ref. [3]. The experimental conditions used in our study were checked to fulfill the requirement of lattice matched growth of the structures. In the present contribution we will report on MOVPE of GaInAs selectively embedded in recesses etched in InP substrates. In particular, the dependence of the growth habit on the orientation and the geometry of the grooves was studied. We also looked into the effect of these factors on the doping during selective growth of GaInAs using DEZn (diethyl zinc, Zn(C2H5)2) and H2S as sources,
2. Experimental Selective embedded growth of GaInAs was carned out in recesses (1.2—2 ~zm deep) in InP sub-
~
strates ([100] oriented, iron doped) fabricated by wet chemical etching (HC1: HNO3 : H20, 2: 1: 1) or RIE (reactive ion etching) [4] through photolithographically defined windows in previously deposited masking layers. Two types of masks were used: Si02 and SjO~Nz.They gave identical resuIts. Growth on these partially masked substrates was performed in a conventional horizontal MOVPE reactor using the precursors TMG (tnmethylgallium, Ga(CH3)3), TMI (trimethylindium, In(CH3)3), AsH3 and PH3 at reduced total pressure (20 hPa), high gas velocity (1.2 m/s) and a growth temperature of 940 K. In order to study the growth history in the recesses, for most runs InP marker layers were incorporated. The masks contained 10 ~tm stripes with different o~rientations (e.g. [011], [010] and [011]) on the surface; the distance between the stripes was at least 100 j.tm. In situ doping of planar substrates was car-
~—
a—.
Fig. 1. GalnAs stripcs selectively embedded in dry etched reLes~esfor different orientations (a) (011). (h) (011) (010), (c) (010) and (d) (011).
150
turned towards
0. Kayser et a!.
/
Selective embedded growth of GaInAs by low pressure MOVPE
tied out using H2S and DEZn. The characterization of the electrical properties of the films was done by Hall measurements. For this purpose the mask was provided with cross shaped windows with a strip width of 100 ~tm.
3. Results and discussion 3.1. Growth in dry etched recesses Fig. 1 demonstrates that selective embedded deposition of GaInAs in previously (dry) etched recesses is feasible. In all cases the micrographs reveal planar surfaces. To show the role of orientation, selectively refilled stripes oriented in different directions are included in the mask. The cleavage surface was etched in H2S04: H202 : H20 to
__
~
~
143
remove approximately 1 ism of the GaInAs layer. During this procedure the surface of the stripes and the mask were covered by a photoresist layer. No preferential etching at the vertical boundaries can be seen; this indicates that there is intimate contact between the epitaxial layers and the InP substrate along the entire surface. In contrast to the (011) oriented stripes, where a wave-like morphology occurs, the other orientations reveal very smooth surfaces. This different behavior indicates that the growth habit in the recesses depends on the orientation of the sidewalls. Thus, details of the growth at the vertical interfaces are of considerable importance. In order to monitor the development of growth at these boundaries, time resolved growth studies were performed. For this purpose, after growing approximately 200 nm the process was interrupted
~
__
~
___
..~
~.1.Cil
~.,
____
Fig. 2. GaInAs/InP heterostructures embedded in dry etched recesses for different orientations (a) (011), (b) (011) towards (010), (c) (010) and (d) (011).
.,~
150
turned
144
/ Selective embedded growth of GalnAs by lowpressure
0. Kayser et a!.
MOVPE
to deposit a thin film (100 nm) of InP. Apart from their potential to display the growth evolution with time, such heterostructures may be used in different types of devices. Fig. 2 shows cleavage
that radiation damage incurred during RIE does not impede epitaxial growth. Probably, this damage is annealed during the heat up of the sample in a PH3 atmosphere before starting the
sections of InP/GaInAs structures for the same orientations as used in fig. 1. The InP marker layers (bright lines) are clearly visible. It may be seen that smooth growth takes place at the GaInAs/InP and InP/GaInAs interfaces, The GaInAs growth rate on the sidewalls is a function of the orientation of the stripes. Whereas for the (011) and (011) directions deposition takes place almost exclusively on the (100) bottom plane, significant growth at the sidewalls occurs if the stripes are oriented in the (010) direction. The latter type of behavior offers the possibility to fabricate embedded structures which are insulated from the substrate. The micrographs also indicate
deposition [5]. Despite the differences in the growth of the heterojunctions near the sidewalls, the stripes display very similar surface morphologies. Note that in all cases there is accelerated growth at the edges leading to the formation of ridges. This behavior is clearly connected to the presence of the InP layers. Indeed, ridge growth was reported for the deposition of InP stripes in the openings of partially masked InP substrates [6,7]. Recent studies indicate that this behavior is caused by diffusive transport of additional group III species from the gas phase above the mask region to the recesses [3,7]. It appears that particularly the In species,
.~
~
.1~..
~
~
~
~
Fig. 3. GaInAs/InP heterostructures embedded in wet chemically etched recesses for_different orientations (a) (011), (b) (011) 150 turned towards (010), (c) (010) and (d) (011).
/ Selective embedded growth of GaInAs by low pressure MOVPE
0. Kayser et a!.
once adsorbed on the semiconductor, have a relatively low surface mobility. This mobility is not sufficient to allow homogeneous distribution over the entire structure, so that ridge growth at the edges results. It should be remarked that pronounced structures like ridges will cause problems in the further processing of the samples. A straightforward way of avoiding ridges is to utilize a shape of the recess, which is able to accommodate the excess material available near the edges. Such alternatively shaped recesses may be obtained using wet chemical etching.
It may be seen that two types of trenches occur: Stripes oriented in (011) direction reveal almost vertical sidewalls, i.e. a U-shaped cross section, similar to the commonly observed shape in the dry etched samples (fig. 3a). In contrast to the RIE case, undercutting of the dielectric layer by approximately 1 ~tm is obtained. The same behavior is also found in fig. 3b for the (011) orientation turned 150 towards (010). On the other hand, stripes oriented in the (010) direction exhibit slanted side walls, i.e. a V-shape cross section. Finally, for the (011) direction the stripes are limited by (111)A planes (V type). There is no underetching of the dielectric layer as for the other orientations. A striking feature is the strong dependence of the shape of the embedded semiconductor layers on the orientation of the stripes. A similar behavion was reported in a study dealing with selective growth of InP on wet chemically etched substrates [8]. Clearly, this is caused by the different shapes of the etched structures. Note that for the (011) direction, where dry and wet chemical etching yield similar shapes of the recesses, the growth
3.2. Growth in wet chemical etched recesses Fig. 3 shows embedded GaInAs/InP structures selectively grown in InP at the same conditions as used for the samples of fig. 2. However, in the present case the stripes were fabricated by wet chemical etching. To facilitate comparison, the same patterns were used as for RIE and again 1.2 ~.tm of the InP substrate was removed in the openings of the masking layer.
I
1018
145
1111111
1111111
I
I
1111111
~
~ 1016 ~ 1
io~
11111111
11111111
I
102
1111111
io°
partial pressure [Pa] Fig. 4. (0) n-type doping level of selectively grown GaInAs versus H
2S partial pressure (stripe width 100 jsm). of selectively grown GaInAs versus DEZn partial pressure (stripe width 100 ~sm).
(~)p-type doping level
146
0. Kayser eta!.
/ Selective embedded growth of GalnAs by low pressure MOVPE
profile is nearly identical. In both cases deposition is strongly hampered on the sidewall and appears almost completely limited to the bottom of the trench. However, for the wet etched trench the surface appears to be planarized in a nearly perfect manner. Along with earlier publications on the growth of InP in InP trenches [7], we propose that the shape of the trench is responsible for this behavior by accomodating the excess material, as discussed above. As expected, this behaviour was found to be independent of the width of the stripes. The same mechanism appears to produce the planar surfaces in figs. 3b and 3c. In contrast,
the sidewalls) is dependent on the orientation of the recesses. When only GaInAs is grown, the surfaces of the stripes tend to be flat. On the other hand, in GaInAs/InP heterostructures pronounced ridge growth occurs at the edges. This different behavior is most likely caused by the different mobility of the reactant species (In versus In/Ga) on the surface in the two cases. Ridge growth may be avoided by using a geometry of the etched recess which accommodates excess material available at the edges. Doping during deposition may be performed in a simple manner using H2S or DEZn. The doping
for the (011) oriented trench, where no underetching occurs, the accumulation of material results in ridge growth at the edges.
level is independent of the size of the structure. Our findings indicate that low pressure MOVPE is capable of producing structures required for monolithic integration of optoelectronic devices.
4. Doping Acknowledgements Doping of GaInAs layers during selective growth was performed using H2S or DEZn. The deposition conditions were the same as those used for the experiments discussed earlier in this paper. The data show a linear relationship between the pressure of the dopant source and carrier concentration in the film (fig. 4). These results are quantitatively similar to data obtained on unstructured samples grown at the same conditions 2/V.[9]. S, The 300 K mobilities (IL300K 10,000 cm ~30OK 6 x iO~cm3 and /1300K 180 cm2/V’
The authors would like to thank A. Brauers and M. Weyers for fruitful discussion and A. Krings for assistance in SEM characterization of the sample morphology. This work was supported by the Bundesministerium für Forschung und Technologie (BMFT) under contract No. TK 04477. References
=
=
=
9 X 10~ cm~3) indicate that the doped layers are somewhat compensated. To check for possible effects of the size of selectively grown structures on the doping level, we carried out p and n doping experiments on cross shaped masks with different widths of the crossed stripes (25, 50 and 100 ~tm). The doping level appeared to be independent on the size of the structure both for n- and p-type samples.
P300K
=
5. Conclusions Our study shows that selective embedded growth of GaInAs stripes in recesses in masked InP substrates is feasible. The mode of deposition (growth only on the bottom surface or also along
[1] H.-J. Yoo, JR. Hayes, C. Caneau, R. Bhat and M. Koza. Electron. Letters 25 (1989) 191. [2] J.S.C. Chang, K.W. Carey, J.E. Turner and L.A. Hodge. presented at 4th Workshop on Organometallic Vapor Phase Epitaxy, Monterey, CA, 1989. [3] J. Finders, J. Geurts, A. Kohl, M. Weyers, B. Opitz, 0. Kayser and P. Balk, J. Crystal Growth 107 (1991) 151. [4] U. Niggebrugge, M. Kiug and G. Garus, in: Proc. 12th Intern. Symp. on GaAs and Related Compounds, Karuizawa, 1985, Inst. Phys. Conf. Ser. 79. Ed. M. Fujimoto (Inst. Phys., London_Bristol, 1986) p. 367. [5] L. Henry, C. Vaudry, Le Corre, D. Lecrosnier. P. Alnot and J. Olivier, Electron. Letters 25 (1989) 1257. [6] A.R. Clawson, C.M. Hanson and T.T. Vu, J. Crystal Growth 77 (1986) 334. [7] K. Nakas, T. Sanada and S. Yamakoshi. J. Crystal Growth 93 (1988) 248. [8] C. Blaauw, A. Szaplonczay, K. Fox and B. Emmersdorfer, J. Crystal Growth 77 (1986) 326. [9] D. Grutzmacher, private communication.
141
Selective embedded growth of GaInAs by low pressure MOVPE 0. Kayser, B. Opitz, R. Westphalen Institute of Semiconductor Electronics, Technical University of Aachen, D-5100 Aachen, Fed. Rep. of Germany
U. Niggebrugge, K. Schneider Heinrich-Heriz-Institut Berlin, D-1000 Berlin, Germany
and P. Balk Institute of Semiconductor Electronics, Technical University of Aachen, D-5100 Aac/zen, Fed. Rep. of Germany
The study reported on in this paper is concerned with selective low pressure (20 hPa) MOVPE of GaInAs and GaInAs/InP heterostructures at 940 K in etched recesses in partially masked substrates. Different growth behavior is obtained for the single layers of the ternary and binary/ternary heterostructures. Moreover, the shape of the recesses, which is related to the etching procedure, also affects the cross section of the deposited stripes. Proper choice of the shape of the recesses permits the growth of planar stripes. The feasibility of in-Situ doping of the GaInAs stripes using H 2S or DEZn is demonstrated.
1. Introduction Selective MOVPE (metalorgamc chemical vapor epitaxy) of InP-based compounds is an attractive technique to produce monolithic integration of electronic and optoelectronic devices [1]. One potential application, butt coupling of optical and electrical components (e.g. waveguide/photodiode), requires the regrowth into recessed areas in previously deposited semiconductor films. Moreover, restriction of the deposition process to recesses offers the potential to achieve monolithic integration of electrically insulated films maintaining an overall planar surface. From the application point of view, planar surfaces are necessary for subsequent metallization and lithography steps. Thus, this technology has the potential for the fabrication of a variety of advanced devices and circuits. For butt coupled waveguide/photodiode combinations, the existence of epitaxial contact be0022-0248/91/$03.50 © 1991
—
tween the embedded material and its surroundings is essential, if high optical losses at the heterointerface are to be avoided. The concept to use a regrown structure as a photodiode implies that doping of selectively deposited material is feasible. Post growth doping may render the fabrication of compact devices more difficult. For the deposition of such doped layers, but also for the growth of heterostructures, knowledge of the details of the growth process is essential. Specifically, it will have to be determined if growth takes place only parallel to the bottom of the recesses, or also on the vertical side walls. In general, optical devices require low densities of misfit dislocations of the epitaxial layers in order to avoid non-radiative transitions. This implies lattice matched growth in combination with minimum variation of the composition in the layers. It has already been reported that the composition of selectively grown GaInAs strongly depends on the geometry of the mask [2]. For details
Elsevier Science Publishers B.V. (North-Holland)
142
0. Kayser et a!.
/ Selective embedded growth of GalnAs by low pressure MO VPE
with respect to this question, see ref. [3]. The experimental conditions used in our study were checked to fulfill the requirement of lattice matched growth of the structures. In the present contribution we will report on MOVPE of GaInAs selectively embedded in recesses etched in InP substrates. In particular, the dependence of the growth habit on the orientation and the geometry of the grooves was studied. We also looked into the effect of these factors on the doping during selective growth of GaInAs using DEZn (diethyl zinc, Zn(C2H5)2) and H2S as sources,
2. Experimental Selective embedded growth of GaInAs was carned out in recesses (1.2—2 ~zm deep) in InP sub-
~
strates ([100] oriented, iron doped) fabricated by wet chemical etching (HC1: HNO3 : H20, 2: 1: 1) or RIE (reactive ion etching) [4] through photolithographically defined windows in previously deposited masking layers. Two types of masks were used: Si02 and SjO~Nz.They gave identical resuIts. Growth on these partially masked substrates was performed in a conventional horizontal MOVPE reactor using the precursors TMG (tnmethylgallium, Ga(CH3)3), TMI (trimethylindium, In(CH3)3), AsH3 and PH3 at reduced total pressure (20 hPa), high gas velocity (1.2 m/s) and a growth temperature of 940 K. In order to study the growth history in the recesses, for most runs InP marker layers were incorporated. The masks contained 10 ~tm stripes with different o~rientations (e.g. [011], [010] and [011]) on the surface; the distance between the stripes was at least 100 j.tm. In situ doping of planar substrates was car-
~—
a—.
Fig. 1. GalnAs stripcs selectively embedded in dry etched reLes~esfor different orientations (a) (011). (h) (011) (010), (c) (010) and (d) (011).
150
turned towards
0. Kayser et a!.
/
Selective embedded growth of GaInAs by low pressure MOVPE
tied out using H2S and DEZn. The characterization of the electrical properties of the films was done by Hall measurements. For this purpose the mask was provided with cross shaped windows with a strip width of 100 ~tm.
3. Results and discussion 3.1. Growth in dry etched recesses Fig. 1 demonstrates that selective embedded deposition of GaInAs in previously (dry) etched recesses is feasible. In all cases the micrographs reveal planar surfaces. To show the role of orientation, selectively refilled stripes oriented in different directions are included in the mask. The cleavage surface was etched in H2S04: H202 : H20 to
__
~
~
143
remove approximately 1 ism of the GaInAs layer. During this procedure the surface of the stripes and the mask were covered by a photoresist layer. No preferential etching at the vertical boundaries can be seen; this indicates that there is intimate contact between the epitaxial layers and the InP substrate along the entire surface. In contrast to the (011) oriented stripes, where a wave-like morphology occurs, the other orientations reveal very smooth surfaces. This different behavior indicates that the growth habit in the recesses depends on the orientation of the sidewalls. Thus, details of the growth at the vertical interfaces are of considerable importance. In order to monitor the development of growth at these boundaries, time resolved growth studies were performed. For this purpose, after growing approximately 200 nm the process was interrupted
~
__
~
___
..~
~.1.Cil
~.,
____
Fig. 2. GaInAs/InP heterostructures embedded in dry etched recesses for different orientations (a) (011), (b) (011) towards (010), (c) (010) and (d) (011).
.,~
150
turned
144
/ Selective embedded growth of GalnAs by lowpressure
0. Kayser et a!.
MOVPE
to deposit a thin film (100 nm) of InP. Apart from their potential to display the growth evolution with time, such heterostructures may be used in different types of devices. Fig. 2 shows cleavage
that radiation damage incurred during RIE does not impede epitaxial growth. Probably, this damage is annealed during the heat up of the sample in a PH3 atmosphere before starting the
sections of InP/GaInAs structures for the same orientations as used in fig. 1. The InP marker layers (bright lines) are clearly visible. It may be seen that smooth growth takes place at the GaInAs/InP and InP/GaInAs interfaces, The GaInAs growth rate on the sidewalls is a function of the orientation of the stripes. Whereas for the (011) and (011) directions deposition takes place almost exclusively on the (100) bottom plane, significant growth at the sidewalls occurs if the stripes are oriented in the (010) direction. The latter type of behavior offers the possibility to fabricate embedded structures which are insulated from the substrate. The micrographs also indicate
deposition [5]. Despite the differences in the growth of the heterojunctions near the sidewalls, the stripes display very similar surface morphologies. Note that in all cases there is accelerated growth at the edges leading to the formation of ridges. This behavior is clearly connected to the presence of the InP layers. Indeed, ridge growth was reported for the deposition of InP stripes in the openings of partially masked InP substrates [6,7]. Recent studies indicate that this behavior is caused by diffusive transport of additional group III species from the gas phase above the mask region to the recesses [3,7]. It appears that particularly the In species,
.~
~
.1~..
~
~
~
~
Fig. 3. GaInAs/InP heterostructures embedded in wet chemically etched recesses for_different orientations (a) (011), (b) (011) 150 turned towards (010), (c) (010) and (d) (011).
/ Selective embedded growth of GaInAs by low pressure MOVPE
0. Kayser et a!.
once adsorbed on the semiconductor, have a relatively low surface mobility. This mobility is not sufficient to allow homogeneous distribution over the entire structure, so that ridge growth at the edges results. It should be remarked that pronounced structures like ridges will cause problems in the further processing of the samples. A straightforward way of avoiding ridges is to utilize a shape of the recess, which is able to accommodate the excess material available near the edges. Such alternatively shaped recesses may be obtained using wet chemical etching.
It may be seen that two types of trenches occur: Stripes oriented in (011) direction reveal almost vertical sidewalls, i.e. a U-shaped cross section, similar to the commonly observed shape in the dry etched samples (fig. 3a). In contrast to the RIE case, undercutting of the dielectric layer by approximately 1 ~tm is obtained. The same behavior is also found in fig. 3b for the (011) orientation turned 150 towards (010). On the other hand, stripes oriented in the (010) direction exhibit slanted side walls, i.e. a V-shape cross section. Finally, for the (011) direction the stripes are limited by (111)A planes (V type). There is no underetching of the dielectric layer as for the other orientations. A striking feature is the strong dependence of the shape of the embedded semiconductor layers on the orientation of the stripes. A similar behavion was reported in a study dealing with selective growth of InP on wet chemically etched substrates [8]. Clearly, this is caused by the different shapes of the etched structures. Note that for the (011) direction, where dry and wet chemical etching yield similar shapes of the recesses, the growth
3.2. Growth in wet chemical etched recesses Fig. 3 shows embedded GaInAs/InP structures selectively grown in InP at the same conditions as used for the samples of fig. 2. However, in the present case the stripes were fabricated by wet chemical etching. To facilitate comparison, the same patterns were used as for RIE and again 1.2 ~.tm of the InP substrate was removed in the openings of the masking layer.
I
1018
145
1111111
1111111
I
I
1111111
~
~ 1016 ~ 1
io~
11111111
11111111
I
102
1111111
io°
partial pressure [Pa] Fig. 4. (0) n-type doping level of selectively grown GaInAs versus H
2S partial pressure (stripe width 100 jsm). of selectively grown GaInAs versus DEZn partial pressure (stripe width 100 ~sm).
(~)p-type doping level
146
0. Kayser eta!.
/ Selective embedded growth of GalnAs by low pressure MOVPE
profile is nearly identical. In both cases deposition is strongly hampered on the sidewall and appears almost completely limited to the bottom of the trench. However, for the wet etched trench the surface appears to be planarized in a nearly perfect manner. Along with earlier publications on the growth of InP in InP trenches [7], we propose that the shape of the trench is responsible for this behavior by accomodating the excess material, as discussed above. As expected, this behaviour was found to be independent of the width of the stripes. The same mechanism appears to produce the planar surfaces in figs. 3b and 3c. In contrast,
the sidewalls) is dependent on the orientation of the recesses. When only GaInAs is grown, the surfaces of the stripes tend to be flat. On the other hand, in GaInAs/InP heterostructures pronounced ridge growth occurs at the edges. This different behavior is most likely caused by the different mobility of the reactant species (In versus In/Ga) on the surface in the two cases. Ridge growth may be avoided by using a geometry of the etched recess which accommodates excess material available at the edges. Doping during deposition may be performed in a simple manner using H2S or DEZn. The doping
for the (011) oriented trench, where no underetching occurs, the accumulation of material results in ridge growth at the edges.
level is independent of the size of the structure. Our findings indicate that low pressure MOVPE is capable of producing structures required for monolithic integration of optoelectronic devices.
4. Doping Acknowledgements Doping of GaInAs layers during selective growth was performed using H2S or DEZn. The deposition conditions were the same as those used for the experiments discussed earlier in this paper. The data show a linear relationship between the pressure of the dopant source and carrier concentration in the film (fig. 4). These results are quantitatively similar to data obtained on unstructured samples grown at the same conditions 2/V.[9]. S, The 300 K mobilities (IL300K 10,000 cm ~30OK 6 x iO~cm3 and /1300K 180 cm2/V’
The authors would like to thank A. Brauers and M. Weyers for fruitful discussion and A. Krings for assistance in SEM characterization of the sample morphology. This work was supported by the Bundesministerium für Forschung und Technologie (BMFT) under contract No. TK 04477. References
=
=
=
9 X 10~ cm~3) indicate that the doped layers are somewhat compensated. To check for possible effects of the size of selectively grown structures on the doping level, we carried out p and n doping experiments on cross shaped masks with different widths of the crossed stripes (25, 50 and 100 ~tm). The doping level appeared to be independent on the size of the structure both for n- and p-type samples.
P300K
=
5. Conclusions Our study shows that selective embedded growth of GaInAs stripes in recesses in masked InP substrates is feasible. The mode of deposition (growth only on the bottom surface or also along
[1] H.-J. Yoo, JR. Hayes, C. Caneau, R. Bhat and M. Koza. Electron. Letters 25 (1989) 191. [2] J.S.C. Chang, K.W. Carey, J.E. Turner and L.A. Hodge. presented at 4th Workshop on Organometallic Vapor Phase Epitaxy, Monterey, CA, 1989. [3] J. Finders, J. Geurts, A. Kohl, M. Weyers, B. Opitz, 0. Kayser and P. Balk, J. Crystal Growth 107 (1991) 151. [4] U. Niggebrugge, M. Kiug and G. Garus, in: Proc. 12th Intern. Symp. on GaAs and Related Compounds, Karuizawa, 1985, Inst. Phys. Conf. Ser. 79. Ed. M. Fujimoto (Inst. Phys., London_Bristol, 1986) p. 367. [5] L. Henry, C. Vaudry, Le Corre, D. Lecrosnier. P. Alnot and J. Olivier, Electron. Letters 25 (1989) 1257. [6] A.R. Clawson, C.M. Hanson and T.T. Vu, J. Crystal Growth 77 (1986) 334. [7] K. Nakas, T. Sanada and S. Yamakoshi. J. Crystal Growth 93 (1988) 248. [8] C. Blaauw, A. Szaplonczay, K. Fox and B. Emmersdorfer, J. Crystal Growth 77 (1986) 326. [9] D. Grutzmacher, private communication.