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Self limiting growth on nominally oriented (111)A GaAs substrates in atomic layer epitaxy
surface science ELSEVIER
Applied Surface Science 103 (1996) 275-278
Self limiting growth on nominally oriented (111 )A GaAs substrates in atomic layer epitaxy Jeong-Sik Lee *, Sohachi Iwai, Hideo Isshiki, Takashi Meguro, Takuo Sugano, Yoshinobu Aoyagi The lnstitutv
of Physical
and Chemical
Research, 2-i.
Hirosawa,
Wako-shi. Saitama 351-01. Japan
Abstract Layer-by-layer growth on nominally oriented (1ll)A GaAs substrate has been performed by atomic layer epitaxy (ALE). Under enough ASH, feeding, the growth rate saturation of one-fourth monolayer per cycle was observed at the Tp range between 560°C and 600°C and three-eighths of monolayer per cycle at the Tp range below 550°C on (1ll)A substrate. The drastic change of the growth rate saturation at around 550°C indicates some kinds of surface reconstructions or site occupation on (1ll)A surface during ASH, supply.
1. Introduction The nano-structure fabrication technique has made remarkable progress and the size control of fine structure is going to enter to the quantum-mechanical region. In very recent years, much effort has been paid to establish suitable fabrication methods of damage-free quantum structures. The fabrication of self-aligned quantum wire structures using step-flow growth [l] or selective growths on patterned substrates [2] has been studied. In addition, self-assembly quantum dot fabrication [3] is now paid much attention to. However, in these methods, size fluctuation of the structures can still not be negligible. Atomic layer epitaxy (ALE) is one of the most powerful candidates to solve the size fluctuation
* Corresponding author. Tel.: + 8 I-48-462111 4624659: e-mail:[email protected]. 0169-4332/96/$15.00 PII
Copyright
SO 169-4332(96)00459-X
1; fax: + 8 I-48.
0 1996 Published
problem, since the layer thickness is controlled by growth sequence because of the self-limiting mechanism of one monolayer (ML) per cycle [4,5]. The self-limiting mechanism also works to suppress the overgrowth at the edge of terraces or facets. Moreover, the growth mode of alternative source gas supply of ALE enhances the growth selectivity. In spite of the advantages mentioned above, few studies have been done in ALE application for nano-structure fabrication. For promoting the applications, the study in growth control on low Miller index planes such as (110) and (111) is necessary because these planes have been used as steps or facets for nanostructure fabrication using selective growth. We have shown the high growth selectivity between the (1ll)A (zero growth) and (100) or (11l)B surfaces (1 ML/cycle) in a previous paper 161. In addition, it was also confirmed that the crystalline quality of the layers grown on (111) substrate was improved by the ALE method. Mirror-like smooth
by Elsevier Science B.V. All rights reserved.
276
J.-S. Lee et al./Applied
Surface Science 103 (1996) 275-278
surface morphologies can be obtained on both (I 11)A and (111)B substrates in the wide range of growth conditions. However, growth rate control on (1ll)A surfaces has not been established. In this paper, we present the study of the growth rate control of GaAs (1ll)A layers in ALE processes. The growth rate saturation, depending on growth temperature, Tp, was observed on (111)A substrate. Self-limiting of the growth rate below 1 ML/cycle suggests the surface reconstruction originated from capture and desorption balance of ASH, (n = l-3) molecules on (1ll)A surface.
Growth Temperature [‘Cl
Fig. 1. GaAs growth rates on each substrate orientation as a function of q.
2. Experimental Semi-insulated GaAs (1ll)A substrate was used in our experiment. (1ll)B and (100) just oriented GaAs substrates were also used for comparison. A horizontal quartz reactor was used here for the ALE growth experiment. Trimethylgallium (TMG) and arsine (ASH,) were used as source materials. The flows of TMG and ASH, are switched on and off alternatively with H, purge duration. The flow rates of TMG, ASH,, and H, carrier gas were 6 X lo-’ mol/s (0.4 Pa partial pressure), 1.8 X 10m5 mol/s (12 Pa), and 3000 seem (1.44 X lo3 Pa), respectively. The other treatment and the growth condition have been reported in a previous paper [6].
3. Results and discussion Fig. 1 shows the growth rates on each substrate orientation as a function of growth temperature. In a cycle of gas supply, TMG supply was 1 s, TMG evacuation by H, 1 s, ASH, 2 s, and ASH, evacuation 0.5 s, respectively. The ideal growth rate of 1 ML (0.283 nm in the case of (100) direction) per cycle is realized on (100) substrate at the Tg range from 550 to 61O”C, the so-called ‘ALE window’. The growth on (111)B substrate has also an ALE (0.326 nm per cycle) window at q between 550 and 590°C. On the other hand, the growth rate on (1ll)A substrate shows a small value compared with the other substrates and decreases with increasing Tg.
The main reason for a low growth rate on (1ll)A surface is the evaporation enhancement of ASH, molecules because each Ga atom of this surface has only one back bond to the incoming ASH n molecules, whereas there are 2 and 3 bonds on (100) and (1ll)B surfaces. On (1ll)A surface, ASH, molecules have to adsorb with only one bond for 100% As site occupation. Therefore, As molecules on the surface are unstable at the Tg around 600°C and evaporate during H, purge duration time. The growth rate declines not only by raising the q but also by extending the H, purge duration time after ASH, supply, as has been reported 161. On the contrary, the growth rate was independent from the H, purge duration time after TMG supply in the ALE window (550°C < Tg < 600°C) region 171. It indicates that no Ga loss from the As surface seems to take place during growth under ALE conditions. GaMe, (Me = CH,, n = l-3) molecules are rather stable compared with ASH,, because of their low vapor pressure and are still adsorbed on the (111)B surface that has only one As dangling bond per atom for incoming GaMe, molecules. ALE condition was maintained on this surface. Consequently, the growth selectivity only depends on an ASH, desorption. As mentioned above, high growth rate contrast between (1ll)A and (100) or (1ll)B surface can be obtained under the same condition. The very low growth rate of (111)A surface under ALE condition on ( 100) or ( 111 )B surfaces can be applicable for the fabrication of quantum wires or boxes, using selec-
J.-S. Lee et al/Applied 0.5
I 0 550°C
I
I
Surface Science 103 (1996) 275-278
(4
0 56O’c
XT
___-_-__-r________~---_. . T’ three-eighths MUcycle 4 0.3L ~~-L-_o~~___,___~____ T one-fourth MUcycle
II
0.10
,“I,
5
1.I
I,,
I..
I.,
10 AsH3 fe%ing ti%
-
,,I [secy
Growth temperature [“Cl Fig. 2. (a) The growth rate on (I I I)A substrates as a function of ASH, pulse duration and (b) the growth rate saturation dependence on Ts.
tive growth with a high controllability of layer thickness. For example, the fabrication of wire structures on the (1ll)A vicinal surface (consisting of (111)A terraces and (100) steps) is suggested. In this case, growth progresses only at (100) steps for wire structure. However, isotropic growth is desirable for embedding the structures because the step density is small (below a few percentages). It takes much time if the growth progress is only in the step region. Therefore, it is necessary to control not only growth suppression but also planar growth along the (( 111 ))A direction. We have verified the possibility of the layer thickness control on (1ll)A surface. Fig. 2(a) shows the growth rate on the (1ll)A surface as a function of the time of ASH, supply. Mirror-like smooth surface morphologies can be obtained for the samples grown at each T,. The growth rate continuously decreases with increasing Tg in a relatively short ASH, supplying time, as seen in Fig. 1 [6]. However, when ASH, supply is sufficient, the growth rate changes drastically at Tg around 550°C. Growth rate saturation of one-fourth ML/cycle was observed at
277
the Tg range between 560°C and 600°C and threeeighths ML/cycle at the Tg range below 550°C on (1ll)A substrate. As you can see in the figure. the self-limiting mechanism works even on (1ll)A surfaces under the condition that the growth rate is lower than 1 ML/cycle. The value of growth rate saturation maintains constant in a relatively wide Tg range as indicated in Fig. 2(b). Therefore, we can make good use of this property for size control of sample structures in the same way as ALE. The growth rate saturation should be concerned with the site occupation for adsorbent molecules. In other words, some kinds of surface reconstructions affected by the capture and desorption balance of ASH,, molecules on the surface are suggested. It has been predicted by Biegelsen et al., using the theoretical calculation and an ultra-high vacuum scanning tunneling microscope that the As stabilized (2 X 2) reconstruction of GaAs (1ll)A surface grown by molecular beam epitaxy has the As-trimer structure bonded to the underlying Ga plane [8]. According to the above-mentioned theoretical studies, the As-trimer structure is energetically stable under As stabilized conditions and has strong bonding between three As atoms. In this case, surface coverage is three-fourths, that is twice the value of the growth rate at 550°C in our work. The other reason, such as the different surface reconstruction originated from steric hindrance, is considered for low growth rates in the ALE process. However, the comparison between Biegelsen’s model and our results suggest trimer adsorption during ASH, supply at low Tg. On the other hand, the ASH,, molecules cannot stay at the surface as trimers and shift to the monomer adsorption phase as Tg gets higher. It is considered that each ASH, molecule is bonded to three Ga atoms. In this case, the coverage of the ASH, molecule is one-fourth and coincides with that of the ALE process at Tg higher than 560°C. If the different value of the growth rate saturation depends on the state of As adsorption, it should reflect the ASH,, evaporation dependence on Tg. Fig. 3 shows the growth rate as a function of Hz purge time after ASH, supply (fpA\). Any growth decline cannot be observed by extending t,,, at T, lower than 550°C. The result indicates that the ASH,, molecules adsorbed on the surface is stable at 550°C and the quasi-As stabilized condition is maintained
278
J.-S. Lee et al. /Applied
Surface Science 103 (1996) 275-278
15 s of AsH3 feeding
go.4 $0.3
r *\ FO.2 .‘\.\ E
4. Conclusions
r-----l ~_n~~~~~~~~~~~~_,_ T three-eighths MUcycle
‘N
0 55o’c 0 58O’c
5 H2 purging tik![sec] Fig. 3. The dependence of GaAs growth rates on the Hz purge duration time after ASH, supply at each Ts.
even in the H, purge duration. Consequently, the results of no As desorption at 550°C imply that the growth rate value of three-eighths ML/cycle corresponds to the coverage of As site occupation during ASH, supply. The result that shows the As stabilized condition also suggests the existence of the As-trimer structure on the surface under this condition. On the other hand, the growth rate decline can be observed at 580°C. In the first stage of tpAs less than 5 s, the growth rate shows a relatively rapid decrease with increasing H, purge duration time. Thereafter, the growth rate decreases slowly to zero. A similar phenomenon can be observed in the growth on (100) surface. In the case of (100) growth, the growth rate decline saturated at 0.75 ML/cycle, which corresponds to (2 X 4) surface reconstruction in ultrahigh vacuum and even in the case of ALE growth [7,9]. Being different from (100) surface, ASH, molecules on (1ll)A surface cannot stay because of its few bonds for adsorbent As. Therefore, they cannot make any kind of surface reconstruction and evaporate thoroughly. It is not clear what kind of surface reconstruction corresponds with the value of one-fourth and threeeight ML/cycle. However, site occupation conceming the surface reconstruction that originates from difference in stability of ASH, was predicted from these results.
We have grown GaAs layers on (1ll)A substrates with high crystalline quality. The value of the growth rate saturation and the growth rate dependence on tpAs were strongly affected by Tg. From the results, some kinds of As adsorption phases, that is, surface reconstruction was suggested. The precise estimation of the surface reconstruction in the ALE process cannot be done yet. However, it is confirmed that the layer thickness on (1ll)A surface can be controlled by growth sequence whereas the growth rate on the surface does not reach 1 ML/cycle. The high growth selectivity between (1ll)A and (100) or (1ll)B surfaces and the saturation of the growth rate on (1ll)A surface imply that nano-structures, such as quantum wire, can be fabricated by selective ALE growth on the surface consist of these two planes with high controllability. Acknowledgements This work was partially supported by the Special Researchers’ Basic Science Program. References 111T. Fukui and H. Saito, J. Vat. 121D. Leonard, M. Krishnamurthy,
Sci. Technol. B 6 (1988) 1373. CM. Reaves, S.P. Denebaars and P.M. Petroff, Appl. Phys. Lett. 63 (19921 3203. [31 D. Leonard, M. Krishnamurthy, C.M. Reaves, S.P. Denebaars and P.M. Petroff, Appl. Phys. Lett. 63 (1993) 3203. [41 H. Isshiki, Y. Aoyagi, T. Sugano, S. Iwai and T. Meguro, Appl. Phys. Lett. 63 (1993) 1528. [Sl H. Isshiki, Y. Aoyagi, T. Sugano, S. lwai and T. Meguro, Appl. Surf. Sci. 82/83 (1994) 57. [61J.-S. Lee, S. Iwai, H. Isshiki, T. Meguro, T. Sugano and Y. Aoyagi, J. Cryst. Growth 160 (1996) 21. [71 J.-S. Lee, S. Iwai, H. Isshiki, T. Meguro, T. Sugano and Y. Aoyagi, Appl. Phys. Lett. 67 (1995) 1283. 181 D.K. Biegelsen, R.D. Bringans, J.E. Northrup and L.-E. Swartz, Phys. Rev. Lett. 65 452 (1990). [91 Y. Sakuma, M. Ozeki and K. Nakajima, J. Cryst. Growth 130 (19931 147.
Applied Surface Science 103 (1996) 275-278
Self limiting growth on nominally oriented (111 )A GaAs substrates in atomic layer epitaxy Jeong-Sik Lee *, Sohachi Iwai, Hideo Isshiki, Takashi Meguro, Takuo Sugano, Yoshinobu Aoyagi The lnstitutv
of Physical
and Chemical
Research, 2-i.
Hirosawa,
Wako-shi. Saitama 351-01. Japan
Abstract Layer-by-layer growth on nominally oriented (1ll)A GaAs substrate has been performed by atomic layer epitaxy (ALE). Under enough ASH, feeding, the growth rate saturation of one-fourth monolayer per cycle was observed at the Tp range between 560°C and 600°C and three-eighths of monolayer per cycle at the Tp range below 550°C on (1ll)A substrate. The drastic change of the growth rate saturation at around 550°C indicates some kinds of surface reconstructions or site occupation on (1ll)A surface during ASH, supply.
1. Introduction The nano-structure fabrication technique has made remarkable progress and the size control of fine structure is going to enter to the quantum-mechanical region. In very recent years, much effort has been paid to establish suitable fabrication methods of damage-free quantum structures. The fabrication of self-aligned quantum wire structures using step-flow growth [l] or selective growths on patterned substrates [2] has been studied. In addition, self-assembly quantum dot fabrication [3] is now paid much attention to. However, in these methods, size fluctuation of the structures can still not be negligible. Atomic layer epitaxy (ALE) is one of the most powerful candidates to solve the size fluctuation
* Corresponding author. Tel.: + 8 I-48-462111 4624659: e-mail:[email protected]. 0169-4332/96/$15.00 PII
Copyright
SO 169-4332(96)00459-X
1; fax: + 8 I-48.
0 1996 Published
problem, since the layer thickness is controlled by growth sequence because of the self-limiting mechanism of one monolayer (ML) per cycle [4,5]. The self-limiting mechanism also works to suppress the overgrowth at the edge of terraces or facets. Moreover, the growth mode of alternative source gas supply of ALE enhances the growth selectivity. In spite of the advantages mentioned above, few studies have been done in ALE application for nano-structure fabrication. For promoting the applications, the study in growth control on low Miller index planes such as (110) and (111) is necessary because these planes have been used as steps or facets for nanostructure fabrication using selective growth. We have shown the high growth selectivity between the (1ll)A (zero growth) and (100) or (11l)B surfaces (1 ML/cycle) in a previous paper 161. In addition, it was also confirmed that the crystalline quality of the layers grown on (111) substrate was improved by the ALE method. Mirror-like smooth
by Elsevier Science B.V. All rights reserved.
276
J.-S. Lee et al./Applied
Surface Science 103 (1996) 275-278
surface morphologies can be obtained on both (I 11)A and (111)B substrates in the wide range of growth conditions. However, growth rate control on (1ll)A surfaces has not been established. In this paper, we present the study of the growth rate control of GaAs (1ll)A layers in ALE processes. The growth rate saturation, depending on growth temperature, Tp, was observed on (111)A substrate. Self-limiting of the growth rate below 1 ML/cycle suggests the surface reconstruction originated from capture and desorption balance of ASH, (n = l-3) molecules on (1ll)A surface.
Growth Temperature [‘Cl
Fig. 1. GaAs growth rates on each substrate orientation as a function of q.
2. Experimental Semi-insulated GaAs (1ll)A substrate was used in our experiment. (1ll)B and (100) just oriented GaAs substrates were also used for comparison. A horizontal quartz reactor was used here for the ALE growth experiment. Trimethylgallium (TMG) and arsine (ASH,) were used as source materials. The flows of TMG and ASH, are switched on and off alternatively with H, purge duration. The flow rates of TMG, ASH,, and H, carrier gas were 6 X lo-’ mol/s (0.4 Pa partial pressure), 1.8 X 10m5 mol/s (12 Pa), and 3000 seem (1.44 X lo3 Pa), respectively. The other treatment and the growth condition have been reported in a previous paper [6].
3. Results and discussion Fig. 1 shows the growth rates on each substrate orientation as a function of growth temperature. In a cycle of gas supply, TMG supply was 1 s, TMG evacuation by H, 1 s, ASH, 2 s, and ASH, evacuation 0.5 s, respectively. The ideal growth rate of 1 ML (0.283 nm in the case of (100) direction) per cycle is realized on (100) substrate at the Tg range from 550 to 61O”C, the so-called ‘ALE window’. The growth on (111)B substrate has also an ALE (0.326 nm per cycle) window at q between 550 and 590°C. On the other hand, the growth rate on (1ll)A substrate shows a small value compared with the other substrates and decreases with increasing Tg.
The main reason for a low growth rate on (1ll)A surface is the evaporation enhancement of ASH, molecules because each Ga atom of this surface has only one back bond to the incoming ASH n molecules, whereas there are 2 and 3 bonds on (100) and (1ll)B surfaces. On (1ll)A surface, ASH, molecules have to adsorb with only one bond for 100% As site occupation. Therefore, As molecules on the surface are unstable at the Tg around 600°C and evaporate during H, purge duration time. The growth rate declines not only by raising the q but also by extending the H, purge duration time after ASH, supply, as has been reported 161. On the contrary, the growth rate was independent from the H, purge duration time after TMG supply in the ALE window (550°C < Tg < 600°C) region 171. It indicates that no Ga loss from the As surface seems to take place during growth under ALE conditions. GaMe, (Me = CH,, n = l-3) molecules are rather stable compared with ASH,, because of their low vapor pressure and are still adsorbed on the (111)B surface that has only one As dangling bond per atom for incoming GaMe, molecules. ALE condition was maintained on this surface. Consequently, the growth selectivity only depends on an ASH, desorption. As mentioned above, high growth rate contrast between (1ll)A and (100) or (1ll)B surface can be obtained under the same condition. The very low growth rate of (111)A surface under ALE condition on ( 100) or ( 111 )B surfaces can be applicable for the fabrication of quantum wires or boxes, using selec-
J.-S. Lee et al/Applied 0.5
I 0 550°C
I
I
Surface Science 103 (1996) 275-278
(4
0 56O’c
XT
___-_-__-r________~---_. . T’ three-eighths MUcycle 4 0.3L ~~-L-_o~~___,___~____ T one-fourth MUcycle
II
0.10
,“I,
5
1.I
I,,
I..
I.,
10 AsH3 fe%ing ti%
-
,,I [secy
Growth temperature [“Cl Fig. 2. (a) The growth rate on (I I I)A substrates as a function of ASH, pulse duration and (b) the growth rate saturation dependence on Ts.
tive growth with a high controllability of layer thickness. For example, the fabrication of wire structures on the (1ll)A vicinal surface (consisting of (111)A terraces and (100) steps) is suggested. In this case, growth progresses only at (100) steps for wire structure. However, isotropic growth is desirable for embedding the structures because the step density is small (below a few percentages). It takes much time if the growth progress is only in the step region. Therefore, it is necessary to control not only growth suppression but also planar growth along the (( 111 ))A direction. We have verified the possibility of the layer thickness control on (1ll)A surface. Fig. 2(a) shows the growth rate on the (1ll)A surface as a function of the time of ASH, supply. Mirror-like smooth surface morphologies can be obtained for the samples grown at each T,. The growth rate continuously decreases with increasing Tg in a relatively short ASH, supplying time, as seen in Fig. 1 [6]. However, when ASH, supply is sufficient, the growth rate changes drastically at Tg around 550°C. Growth rate saturation of one-fourth ML/cycle was observed at
277
the Tg range between 560°C and 600°C and threeeighths ML/cycle at the Tg range below 550°C on (1ll)A substrate. As you can see in the figure. the self-limiting mechanism works even on (1ll)A surfaces under the condition that the growth rate is lower than 1 ML/cycle. The value of growth rate saturation maintains constant in a relatively wide Tg range as indicated in Fig. 2(b). Therefore, we can make good use of this property for size control of sample structures in the same way as ALE. The growth rate saturation should be concerned with the site occupation for adsorbent molecules. In other words, some kinds of surface reconstructions affected by the capture and desorption balance of ASH,, molecules on the surface are suggested. It has been predicted by Biegelsen et al., using the theoretical calculation and an ultra-high vacuum scanning tunneling microscope that the As stabilized (2 X 2) reconstruction of GaAs (1ll)A surface grown by molecular beam epitaxy has the As-trimer structure bonded to the underlying Ga plane [8]. According to the above-mentioned theoretical studies, the As-trimer structure is energetically stable under As stabilized conditions and has strong bonding between three As atoms. In this case, surface coverage is three-fourths, that is twice the value of the growth rate at 550°C in our work. The other reason, such as the different surface reconstruction originated from steric hindrance, is considered for low growth rates in the ALE process. However, the comparison between Biegelsen’s model and our results suggest trimer adsorption during ASH, supply at low Tg. On the other hand, the ASH,, molecules cannot stay at the surface as trimers and shift to the monomer adsorption phase as Tg gets higher. It is considered that each ASH, molecule is bonded to three Ga atoms. In this case, the coverage of the ASH, molecule is one-fourth and coincides with that of the ALE process at Tg higher than 560°C. If the different value of the growth rate saturation depends on the state of As adsorption, it should reflect the ASH,, evaporation dependence on Tg. Fig. 3 shows the growth rate as a function of Hz purge time after ASH, supply (fpA\). Any growth decline cannot be observed by extending t,,, at T, lower than 550°C. The result indicates that the ASH,, molecules adsorbed on the surface is stable at 550°C and the quasi-As stabilized condition is maintained
278
J.-S. Lee et al. /Applied
Surface Science 103 (1996) 275-278
15 s of AsH3 feeding
go.4 $0.3
r *\ FO.2 .‘\.\ E
4. Conclusions
r-----l ~_n~~~~~~~~~~~~_,_ T three-eighths MUcycle
‘N
0 55o’c 0 58O’c
5 H2 purging tik![sec] Fig. 3. The dependence of GaAs growth rates on the Hz purge duration time after ASH, supply at each Ts.
even in the H, purge duration. Consequently, the results of no As desorption at 550°C imply that the growth rate value of three-eighths ML/cycle corresponds to the coverage of As site occupation during ASH, supply. The result that shows the As stabilized condition also suggests the existence of the As-trimer structure on the surface under this condition. On the other hand, the growth rate decline can be observed at 580°C. In the first stage of tpAs less than 5 s, the growth rate shows a relatively rapid decrease with increasing H, purge duration time. Thereafter, the growth rate decreases slowly to zero. A similar phenomenon can be observed in the growth on (100) surface. In the case of (100) growth, the growth rate decline saturated at 0.75 ML/cycle, which corresponds to (2 X 4) surface reconstruction in ultrahigh vacuum and even in the case of ALE growth [7,9]. Being different from (100) surface, ASH, molecules on (1ll)A surface cannot stay because of its few bonds for adsorbent As. Therefore, they cannot make any kind of surface reconstruction and evaporate thoroughly. It is not clear what kind of surface reconstruction corresponds with the value of one-fourth and threeeight ML/cycle. However, site occupation conceming the surface reconstruction that originates from difference in stability of ASH, was predicted from these results.
We have grown GaAs layers on (1ll)A substrates with high crystalline quality. The value of the growth rate saturation and the growth rate dependence on tpAs were strongly affected by Tg. From the results, some kinds of As adsorption phases, that is, surface reconstruction was suggested. The precise estimation of the surface reconstruction in the ALE process cannot be done yet. However, it is confirmed that the layer thickness on (1ll)A surface can be controlled by growth sequence whereas the growth rate on the surface does not reach 1 ML/cycle. The high growth selectivity between (1ll)A and (100) or (1ll)B surfaces and the saturation of the growth rate on (1ll)A surface imply that nano-structures, such as quantum wire, can be fabricated by selective ALE growth on the surface consist of these two planes with high controllability. Acknowledgements This work was partially supported by the Special Researchers’ Basic Science Program. References 111T. Fukui and H. Saito, J. Vat. 121D. Leonard, M. Krishnamurthy,
Sci. Technol. B 6 (1988) 1373. CM. Reaves, S.P. Denebaars and P.M. Petroff, Appl. Phys. Lett. 63 (19921 3203. [31 D. Leonard, M. Krishnamurthy, C.M. Reaves, S.P. Denebaars and P.M. Petroff, Appl. Phys. Lett. 63 (1993) 3203. [41 H. Isshiki, Y. Aoyagi, T. Sugano, S. Iwai and T. Meguro, Appl. Phys. Lett. 63 (1993) 1528. [Sl H. Isshiki, Y. Aoyagi, T. Sugano, S. lwai and T. Meguro, Appl. Surf. Sci. 82/83 (1994) 57. [61J.-S. Lee, S. Iwai, H. Isshiki, T. Meguro, T. Sugano and Y. Aoyagi, J. Cryst. Growth 160 (1996) 21. [71 J.-S. Lee, S. Iwai, H. Isshiki, T. Meguro, T. Sugano and Y. Aoyagi, Appl. Phys. Lett. 67 (1995) 1283. 181 D.K. Biegelsen, R.D. Bringans, J.E. Northrup and L.-E. Swartz, Phys. Rev. Lett. 65 452 (1990). [91 Y. Sakuma, M. Ozeki and K. Nakajima, J. Cryst. Growth 130 (19931 147.