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Influence of substrate conductivity type on the thickness and composition of epitaxial layers grown by Liquid Phase Epitaxy
Thin Solid Films 520 (2011) 700–702
Contents lists available at ScienceDirect
Thin Solid Films j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t s f
Influence of substrate conductivity type on the thickness and composition of epitaxial layers grown by Liquid Phase Epitaxy E. Momox-Beristain a, J. Martínez-Juárez a, F. de Anda b,⁎, V.H. Compeán-Jasso b, V.A. Mishurnyi b, G. Juárez-Díaz c a b c
CIDS-ICUAP-BUAP. Apartado Postal 207, 72000 Puebla, Pue., Mexico Universidad Autónoma de San Luis Potosí, Instituto de Investigación en Comunicación Óptica, Av. Karakorum 1470, Col. Lomas 4a Sec., San Luis Potosí, SLP, CP 78210, Mexico CINVESTAV-IPN, Av. IPN 2508, Col. San Pedro Zacatenco, México D.F., CP 07360, Mexico
a r t i c l e
i n f o
Available online 2 February 2011 Keywords: Liquid Phase Epitaxy (LPE) Growth kinetics Liquid–solid interfaces
a b s t r a c t It is shown that the conductivity of the substrate has a non negligible effect on the thickness and composition of epitaxial layers grown by Liquid Phase Epitaxy. The growth experiments have been done on the systems GaAs/GaAs, GaAlSb/GaSb and GaInAsSb/GaSb. To insure strictly the same growth conditions the growth was done simultaneously, from the same liquid phase, on the different substrates. © 2011 Elsevier B.V. All rights reserved.
1. Introduction When epitaxial layers are to be grown by Liquid Phase Epitaxy (LPE) it is normally assumed that the growth speed depends only on the liquid supersaturation, the temperature and the cooling rate of the liquid and substrate. However it is well known that the growth rate of a crystal depends also on other factors such as the crystallographic orientation of the substrate, temperature gradients, etc. In the case of heteroepitaxy, the composition of the grown layer depends mainly on the phase diagram of the material to be grown but it has been shown that its composition also depends on other parameters such as: crystallographic orientation of the substrate, lattice mismatch, etc. We have noticed that the conductivity type of the substrate has a measurable effect on the layer thickness and chemical composition of layers grown by LPE. Here we review the results of previous work concerning the growth of GaAs on GaAs [1] at several temperatures and growth times and GaAlSb on GaSb [2] from a single liquid composition at fixed temperature and several growth times. In the first case it is shown that the thickness of GaAs epitaxial layers differ when they are grown on substrates of different conductivity and carrier concentration and that the magnitude of the difference changes with the growth temperature. In the case of GaAlSb the same effect is present but additionally a change in chemical composition is also observed. Some preliminary results concerning the growth of GaInAsSb on GaSb show that these effects take place also in this system. The poor reproducibility of the thickness of epitaxial layers grown by LPE is a well known problem. In order to demonstrate, without any
⁎ Corresponding author. E-mail address: [email protected] (F. de Anda). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.01.352
doubt, the differences introduced by substrates of different conductivities during LPE it is necessary to do the growth experiments under exactly the same conditions. The variation of the thickness of the layers, even when they are grown under the same nominal conditions is normally attributed to small differences in growth temperature, liquid supercooling, temperature gradients, growth time, etc. that normally occur from one experiment to another one. As a consequence of the poor reproducibility of the LPE growth it is not convenient to compare the results of any two different experiments if the goal is to study small differences between experiments intended to be done under the same conditions. In order to avoid these uncertainties and to grow the layers on different substrates but under strictly the same conditions we have performed the growth experiments simultaneously from the same liquid solution and placing the substrates side by side in the slider. In this way we insure that the growth on both substrates is done under strictly the same experimental conditions.
2. Experimental details The growth experiments were done in a graphite boat, in a horizontal reactor, under a 0.5 lt/min flow of Pd-diffused hydrogen, inside a semitransparent furnace. The substrates were placed side by side in the graphite slider used to put all the substrates in contact with the same liquid solution. The substrates used for the growth of GaAs layers were: P-Type GaAs:Zn with a free hole concentration of 1 × 1019 cm− 3, N type GaAs:Te with a free electron concentration of 1 × 1017 cm− 3 and Semi-Insulating (SI) substrate was non-doped GaAs with a resistivity larger than 107 Ω cm. In this case the growth was done simultaneously in three different substrates, semi-insulating (SI), P-type and N-type.
E. Momox-Beristain et al. / Thin Solid Films 520 (2011) 700–702
20
10
Growth temperature=786 °C Imposed supercooling= 15 °C
intensity (counts/s)
Fitted Supercoolings
15
Thickness (μm)
10
ΔT P = 10.8 C ΔT N = 7.8 C ΔT SI= 5.7 C
10
P type substrate
5
10 10 10 10
N type substrate SI type substrate
6
5
N type substrate P type substrate
4
3
2
1
0
10
30.2
0 0
200
400
600
701
30.3
30.4
30.5
ω (degrees)
800
Time (sec) Fig. 1. Thickness of GaAs layers grown at 786 °C on P-type, N-type and semi-insulating GaAs substrates.
In the case of GaAlSb the liquid solution consisted of 6 N Ga and Al and 5 N GaSb and its composition was fixed to XGa =0.986 and XAl =0.002. The liquidus temperature was 450 °C, before establishing the contact the liquid was supercooled by 10 °C and the temperature was held constant during the growth time. Growth times ranged from 20 s to 600 s. The N type substrates were Te doped GaSb with a free carrier concentration of (1.1–4.0)×1017 cm− 3 and the P type substrates were Zn doped GaSb with a free carrier concentration of (1.9–3.0)×1018 cm− 3. In the case of GaInAsSb the substrates were GaSb P-type undoped with a free carrier concentration of (1–2)×1015 cm− 3 the N type substrates were those described above, the growth temperature was 540 °C and the liquidus composition was XGa =0.184, XIn =0.577 and XSb =0.238. All substrates had the (100) orientation and their size was 10 mm×5 mm. All substrates were chemically polished in a mixture of H2O2: HF: C4O6H6 (tartaric acid): H2O just before the growth process [3].
3. Results and discussion The thickness of GaAs layers grown at 786 °C with a nominal supercooling of 15 °C and several growth times are shown in Fig. 1, the size of the symbols indicate the variations of the thickness measured within each sample. It can be seen that the thicker layers grow on the P-type substrates and that the thinner layers grow on the SI substrates.
15
Thickness (μm)
12
9
6 Growth time=10min. P type substrates N type substrates SI type substrates
3
650
700
750
In LPE, the thickness of the grown layers as a function of time, d(t), is given by the Hsieh equation [4]. dðt Þ =
1 1 1 D 2 4 3 2ΔTt 2 + Rt 2 Cs m π 3
where Cs is the concentration of As in the solid, m the slope of the liquidus line of the GaAs phase diagram at the growth temperature, D the diffusion coefficient of As in Ga, R the cooling rate and ΔT the initial supercooling . From all of these parameters the only one that could be affected by the substrate is the supercooling so in order to adjust our results to the above equation the only parameter that could change from one substrate to another one is ΔT. The supercooling of the liquid solution ΔT is in fact a measure of its super saturation i.e., of the deviation from the thermodynamic equilibrium between the liquid solution and the substrate. It is known that this equilibrium can be modified by several factors such as the crystallographic orientation, the stress field due to the lattice mismatch, etc. In our case the only difference between the substrates is its conductivity type and carrier concentration and it is known that in GaAs the Fermi Level at the surface is pinned near the middle of the band gap. This pinning produces a surface “band bending” or surface potential different in magnitude for P and N type material its magnitude depends also in the Fermi level position in the bulk i. e. of the carrier concentration [5]. Therefore, we could explain the differences in the “effective” supercooling by proposing that they are produced by an alteration of the equilibrium between the liquid solution and the solid due to the presence of the surface band bending. The position of the Fermi level pinning at the surface it is not well known at the growth temperatures used in this work but if we admit that the pinning position shifts toward the intrinsic Fermi level as the temperature increases but at a different rate in each material as the bulk Fermi level does we could explain the behavior observed in Fig. 2. Table 1 Thickness and composition of epitaxial layers as a function of growth time calculated from the X-ray rocking curves. Growth time (s)
0 600
Fig. 3. Comparison of the HRXRD rocking curves of a couple of Ga1 − xAlxSb layers grown simultaneously on P and N type substrates at 450 °C during 40 s. The inset is a magnification of the peaks to ease the comparison.
800
Temperature (°C) Fig. 2. Differences in growth thicknesses of GaAs layers grown at several temperatures during 10 min. on P-type, N-type and semi-insulating GaAs substrates.
20 40 80 160 320 640
Thickness (μm)
Composition (x)
Type N
Type P
Type N
Type P
0.3 2.0 2.0 5.6 7.8 10.9
0.2 1.4 0.9 4.0 6.5 7.7
0.084 0.063 0.075 0.072 0.087 0.123
0.09 0.068 0.081 0.083 0.088 0.14
702
E. Momox-Beristain et al. / Thin Solid Films 520 (2011) 700–702
0.8
1.0
GaInAsSb/GaSb Substrate
N-Type Substrate P-Type Substrate
Intensity (arb.units)
Intensity (counts/s)
1.0
0.6 0.4 0.2
P-type substrat N-type substrat
0.8
Temperature 40 K 0.6 0.4 0.2 0.0
0.0 30.35
1800
30.40
ω (degrees)
1900
2000
2100
Wavelenght (nm)
Fig. 4. HRXRD rocking curves of GaInAsSb epitaxial layers grown on p and N type GaSb substrates. Growth temperature: 540 °C, growth time: 1 min.
Fig. 5. Photoluminescence spectra of GaInAsSb layers grown simultaneously on N and P-type GaSb substrates.
Then from 600 °C to 740 °C there is a diminishing difference between the layer thicknesses, all layers have almost the same thickness at 740 °C, this could be explained by supposing the surface electric field become similar in magnitude for all three types of substrates. At 786 °C the differences appear again and this could mean that the surface electric fields start to diverge again. An exact explanation of these effects necessarily requires the knowledge of the behavior of the surface Fermi level pinning at high and changing temperature as the ones used for LPE. In the case of Ga1 − xAlxSb the growth was done at a fixed temperature of 450 °C and several growth times, the same effects regarding the thickness of the layers were observed but additionally a change in Al content of the layers was also observed. Fig. 3 compares the HRXRD rocking curves of any couple of layers grown simultaneously on P and N type substrates. It can be seen that there are differences in the thickness and composition of each layer. The differences are small but they appear in all the couples of layers grown simultaneously. A summary of the thickness and composition calculated from the rocking curves using the Takagi-Taupin [6,7] theory is presented in Table 1. We can see small differences in the layers composition even when all the layers were grown from liquid solutions with the “same” nominal composition. This variation are related to the reproducibility problems associated with Liquid Phase Epitaxy as mentioned above, i.e. the weight of each element is not exactly the same from one experiment to another one also the exact growth temperature, supercooling, temperature gradients and growth time may change. However, for the same growth experiment, on N and P type substrates simultaneously, it can be seen that the thickness of the epitaxial layer grown on N type substrate is always larger and its Al content is less than those of the layer grown on P type substrate. In the case of GaSb it is known that the Fermi level at the surface is pinned at about 0.1 eV above the valence band then the electric field at the surface is larger for the N-type substrates than for the P-type. This is in agreement with the results for layers grown on GaAs substrates i.e.,
the thicker layers grow on the substrate where the electric field is larger but in this case in the N GaSb substrate has a smaller free carrier concentration. In the case of GaInAsSb grown on GaSb the same effects are observed as regards the thickness and composition of the epitaxial layers as shown by the HRXRD rocking curves in Fig. 4. In this case, as shown in Fig. 5, the difference in composition has been also observed in the photoluminescence spectra of the epitaxial layers. 4. Conclusions The simultaneous growth of epitaxial layers from the liquid phase on substrates with different conductivity in the systems GaAs/GaAs GaAlSb/GaSb and GaInAsSb/GaSb show that the conductivity of the substrate has a non negligible effect on the properties of the epitaxial layers grown by Liquid Phase Epitaxy. This effect can be, presumably, observed in the LPE growth of other systems as well. Acknowledgements This work was partially supported by CONACYT, PROMEP and FAI at UASLP. References [1] J. Olvera-Hernández, P. de Jesús, F. de Anda, M. Rojas-López, J. Cryst. Growth 268 (2004) 375. [2] E. Momox Beristain, J. Olvera-Hernández, J. Martínez-Juárez, F. de Anda, V.H. Compeán-Jasso, V. A. Mishurnyi, V. H. Méndez-García and G. Juárez-Díaz. Accepted for publication in Thin Solid Films. doi:10.1016/j.tsf.2010.12.018. [3] I.E. Berishev, F. de Anda, V.A. Mishurnyi, J. Olvera, N.D. Ilynskaia, V.I. Vasil'ev, J. Electrochem. Soc. 142 (1995) L189. [4] J.J. Hsieh, J. Cryst. Growth 27 (1974) 49. [5] W.E. Spicer, P.W. Chye, P.R. Skeath, C.Y. Su, I. Lindau, J. Vac. Sci. Technol. 16 (1979) 1422. [6] S. Takagi, J. Phys. Soc. Jap. 26 (1969) 1239. [7] D. Taupin, Bull. Soc. Fran. Miner. Cryst. 87 (1964) 469.
Contents lists available at ScienceDirect
Thin Solid Films j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / t s f
Influence of substrate conductivity type on the thickness and composition of epitaxial layers grown by Liquid Phase Epitaxy E. Momox-Beristain a, J. Martínez-Juárez a, F. de Anda b,⁎, V.H. Compeán-Jasso b, V.A. Mishurnyi b, G. Juárez-Díaz c a b c
CIDS-ICUAP-BUAP. Apartado Postal 207, 72000 Puebla, Pue., Mexico Universidad Autónoma de San Luis Potosí, Instituto de Investigación en Comunicación Óptica, Av. Karakorum 1470, Col. Lomas 4a Sec., San Luis Potosí, SLP, CP 78210, Mexico CINVESTAV-IPN, Av. IPN 2508, Col. San Pedro Zacatenco, México D.F., CP 07360, Mexico
a r t i c l e
i n f o
Available online 2 February 2011 Keywords: Liquid Phase Epitaxy (LPE) Growth kinetics Liquid–solid interfaces
a b s t r a c t It is shown that the conductivity of the substrate has a non negligible effect on the thickness and composition of epitaxial layers grown by Liquid Phase Epitaxy. The growth experiments have been done on the systems GaAs/GaAs, GaAlSb/GaSb and GaInAsSb/GaSb. To insure strictly the same growth conditions the growth was done simultaneously, from the same liquid phase, on the different substrates. © 2011 Elsevier B.V. All rights reserved.
1. Introduction When epitaxial layers are to be grown by Liquid Phase Epitaxy (LPE) it is normally assumed that the growth speed depends only on the liquid supersaturation, the temperature and the cooling rate of the liquid and substrate. However it is well known that the growth rate of a crystal depends also on other factors such as the crystallographic orientation of the substrate, temperature gradients, etc. In the case of heteroepitaxy, the composition of the grown layer depends mainly on the phase diagram of the material to be grown but it has been shown that its composition also depends on other parameters such as: crystallographic orientation of the substrate, lattice mismatch, etc. We have noticed that the conductivity type of the substrate has a measurable effect on the layer thickness and chemical composition of layers grown by LPE. Here we review the results of previous work concerning the growth of GaAs on GaAs [1] at several temperatures and growth times and GaAlSb on GaSb [2] from a single liquid composition at fixed temperature and several growth times. In the first case it is shown that the thickness of GaAs epitaxial layers differ when they are grown on substrates of different conductivity and carrier concentration and that the magnitude of the difference changes with the growth temperature. In the case of GaAlSb the same effect is present but additionally a change in chemical composition is also observed. Some preliminary results concerning the growth of GaInAsSb on GaSb show that these effects take place also in this system. The poor reproducibility of the thickness of epitaxial layers grown by LPE is a well known problem. In order to demonstrate, without any
⁎ Corresponding author. E-mail address: [email protected] (F. de Anda). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.01.352
doubt, the differences introduced by substrates of different conductivities during LPE it is necessary to do the growth experiments under exactly the same conditions. The variation of the thickness of the layers, even when they are grown under the same nominal conditions is normally attributed to small differences in growth temperature, liquid supercooling, temperature gradients, growth time, etc. that normally occur from one experiment to another one. As a consequence of the poor reproducibility of the LPE growth it is not convenient to compare the results of any two different experiments if the goal is to study small differences between experiments intended to be done under the same conditions. In order to avoid these uncertainties and to grow the layers on different substrates but under strictly the same conditions we have performed the growth experiments simultaneously from the same liquid solution and placing the substrates side by side in the slider. In this way we insure that the growth on both substrates is done under strictly the same experimental conditions.
2. Experimental details The growth experiments were done in a graphite boat, in a horizontal reactor, under a 0.5 lt/min flow of Pd-diffused hydrogen, inside a semitransparent furnace. The substrates were placed side by side in the graphite slider used to put all the substrates in contact with the same liquid solution. The substrates used for the growth of GaAs layers were: P-Type GaAs:Zn with a free hole concentration of 1 × 1019 cm− 3, N type GaAs:Te with a free electron concentration of 1 × 1017 cm− 3 and Semi-Insulating (SI) substrate was non-doped GaAs with a resistivity larger than 107 Ω cm. In this case the growth was done simultaneously in three different substrates, semi-insulating (SI), P-type and N-type.
E. Momox-Beristain et al. / Thin Solid Films 520 (2011) 700–702
20
10
Growth temperature=786 °C Imposed supercooling= 15 °C
intensity (counts/s)
Fitted Supercoolings
15
Thickness (μm)
10
ΔT P = 10.8 C ΔT N = 7.8 C ΔT SI= 5.7 C
10
P type substrate
5
10 10 10 10
N type substrate SI type substrate
6
5
N type substrate P type substrate
4
3
2
1
0
10
30.2
0 0
200
400
600
701
30.3
30.4
30.5
ω (degrees)
800
Time (sec) Fig. 1. Thickness of GaAs layers grown at 786 °C on P-type, N-type and semi-insulating GaAs substrates.
In the case of GaAlSb the liquid solution consisted of 6 N Ga and Al and 5 N GaSb and its composition was fixed to XGa =0.986 and XAl =0.002. The liquidus temperature was 450 °C, before establishing the contact the liquid was supercooled by 10 °C and the temperature was held constant during the growth time. Growth times ranged from 20 s to 600 s. The N type substrates were Te doped GaSb with a free carrier concentration of (1.1–4.0)×1017 cm− 3 and the P type substrates were Zn doped GaSb with a free carrier concentration of (1.9–3.0)×1018 cm− 3. In the case of GaInAsSb the substrates were GaSb P-type undoped with a free carrier concentration of (1–2)×1015 cm− 3 the N type substrates were those described above, the growth temperature was 540 °C and the liquidus composition was XGa =0.184, XIn =0.577 and XSb =0.238. All substrates had the (100) orientation and their size was 10 mm×5 mm. All substrates were chemically polished in a mixture of H2O2: HF: C4O6H6 (tartaric acid): H2O just before the growth process [3].
3. Results and discussion The thickness of GaAs layers grown at 786 °C with a nominal supercooling of 15 °C and several growth times are shown in Fig. 1, the size of the symbols indicate the variations of the thickness measured within each sample. It can be seen that the thicker layers grow on the P-type substrates and that the thinner layers grow on the SI substrates.
15
Thickness (μm)
12
9
6 Growth time=10min. P type substrates N type substrates SI type substrates
3
650
700
750
In LPE, the thickness of the grown layers as a function of time, d(t), is given by the Hsieh equation [4]. dðt Þ =
1 1 1 D 2 4 3 2ΔTt 2 + Rt 2 Cs m π 3
where Cs is the concentration of As in the solid, m the slope of the liquidus line of the GaAs phase diagram at the growth temperature, D the diffusion coefficient of As in Ga, R the cooling rate and ΔT the initial supercooling . From all of these parameters the only one that could be affected by the substrate is the supercooling so in order to adjust our results to the above equation the only parameter that could change from one substrate to another one is ΔT. The supercooling of the liquid solution ΔT is in fact a measure of its super saturation i.e., of the deviation from the thermodynamic equilibrium between the liquid solution and the substrate. It is known that this equilibrium can be modified by several factors such as the crystallographic orientation, the stress field due to the lattice mismatch, etc. In our case the only difference between the substrates is its conductivity type and carrier concentration and it is known that in GaAs the Fermi Level at the surface is pinned near the middle of the band gap. This pinning produces a surface “band bending” or surface potential different in magnitude for P and N type material its magnitude depends also in the Fermi level position in the bulk i. e. of the carrier concentration [5]. Therefore, we could explain the differences in the “effective” supercooling by proposing that they are produced by an alteration of the equilibrium between the liquid solution and the solid due to the presence of the surface band bending. The position of the Fermi level pinning at the surface it is not well known at the growth temperatures used in this work but if we admit that the pinning position shifts toward the intrinsic Fermi level as the temperature increases but at a different rate in each material as the bulk Fermi level does we could explain the behavior observed in Fig. 2. Table 1 Thickness and composition of epitaxial layers as a function of growth time calculated from the X-ray rocking curves. Growth time (s)
0 600
Fig. 3. Comparison of the HRXRD rocking curves of a couple of Ga1 − xAlxSb layers grown simultaneously on P and N type substrates at 450 °C during 40 s. The inset is a magnification of the peaks to ease the comparison.
800
Temperature (°C) Fig. 2. Differences in growth thicknesses of GaAs layers grown at several temperatures during 10 min. on P-type, N-type and semi-insulating GaAs substrates.
20 40 80 160 320 640
Thickness (μm)
Composition (x)
Type N
Type P
Type N
Type P
0.3 2.0 2.0 5.6 7.8 10.9
0.2 1.4 0.9 4.0 6.5 7.7
0.084 0.063 0.075 0.072 0.087 0.123
0.09 0.068 0.081 0.083 0.088 0.14
702
E. Momox-Beristain et al. / Thin Solid Films 520 (2011) 700–702
0.8
1.0
GaInAsSb/GaSb Substrate
N-Type Substrate P-Type Substrate
Intensity (arb.units)
Intensity (counts/s)
1.0
0.6 0.4 0.2
P-type substrat N-type substrat
0.8
Temperature 40 K 0.6 0.4 0.2 0.0
0.0 30.35
1800
30.40
ω (degrees)
1900
2000
2100
Wavelenght (nm)
Fig. 4. HRXRD rocking curves of GaInAsSb epitaxial layers grown on p and N type GaSb substrates. Growth temperature: 540 °C, growth time: 1 min.
Fig. 5. Photoluminescence spectra of GaInAsSb layers grown simultaneously on N and P-type GaSb substrates.
Then from 600 °C to 740 °C there is a diminishing difference between the layer thicknesses, all layers have almost the same thickness at 740 °C, this could be explained by supposing the surface electric field become similar in magnitude for all three types of substrates. At 786 °C the differences appear again and this could mean that the surface electric fields start to diverge again. An exact explanation of these effects necessarily requires the knowledge of the behavior of the surface Fermi level pinning at high and changing temperature as the ones used for LPE. In the case of Ga1 − xAlxSb the growth was done at a fixed temperature of 450 °C and several growth times, the same effects regarding the thickness of the layers were observed but additionally a change in Al content of the layers was also observed. Fig. 3 compares the HRXRD rocking curves of any couple of layers grown simultaneously on P and N type substrates. It can be seen that there are differences in the thickness and composition of each layer. The differences are small but they appear in all the couples of layers grown simultaneously. A summary of the thickness and composition calculated from the rocking curves using the Takagi-Taupin [6,7] theory is presented in Table 1. We can see small differences in the layers composition even when all the layers were grown from liquid solutions with the “same” nominal composition. This variation are related to the reproducibility problems associated with Liquid Phase Epitaxy as mentioned above, i.e. the weight of each element is not exactly the same from one experiment to another one also the exact growth temperature, supercooling, temperature gradients and growth time may change. However, for the same growth experiment, on N and P type substrates simultaneously, it can be seen that the thickness of the epitaxial layer grown on N type substrate is always larger and its Al content is less than those of the layer grown on P type substrate. In the case of GaSb it is known that the Fermi level at the surface is pinned at about 0.1 eV above the valence band then the electric field at the surface is larger for the N-type substrates than for the P-type. This is in agreement with the results for layers grown on GaAs substrates i.e.,
the thicker layers grow on the substrate where the electric field is larger but in this case in the N GaSb substrate has a smaller free carrier concentration. In the case of GaInAsSb grown on GaSb the same effects are observed as regards the thickness and composition of the epitaxial layers as shown by the HRXRD rocking curves in Fig. 4. In this case, as shown in Fig. 5, the difference in composition has been also observed in the photoluminescence spectra of the epitaxial layers. 4. Conclusions The simultaneous growth of epitaxial layers from the liquid phase on substrates with different conductivity in the systems GaAs/GaAs GaAlSb/GaSb and GaInAsSb/GaSb show that the conductivity of the substrate has a non negligible effect on the properties of the epitaxial layers grown by Liquid Phase Epitaxy. This effect can be, presumably, observed in the LPE growth of other systems as well. Acknowledgements This work was partially supported by CONACYT, PROMEP and FAI at UASLP. References [1] J. Olvera-Hernández, P. de Jesús, F. de Anda, M. Rojas-López, J. Cryst. Growth 268 (2004) 375. [2] E. Momox Beristain, J. Olvera-Hernández, J. Martínez-Juárez, F. de Anda, V.H. Compeán-Jasso, V. A. Mishurnyi, V. H. Méndez-García and G. Juárez-Díaz. Accepted for publication in Thin Solid Films. doi:10.1016/j.tsf.2010.12.018. [3] I.E. Berishev, F. de Anda, V.A. Mishurnyi, J. Olvera, N.D. Ilynskaia, V.I. Vasil'ev, J. Electrochem. Soc. 142 (1995) L189. [4] J.J. Hsieh, J. Cryst. Growth 27 (1974) 49. [5] W.E. Spicer, P.W. Chye, P.R. Skeath, C.Y. Su, I. Lindau, J. Vac. Sci. Technol. 16 (1979) 1422. [6] S. Takagi, J. Phys. Soc. Jap. 26 (1969) 1239. [7] D. Taupin, Bull. Soc. Fran. Miner. Cryst. 87 (1964) 469.