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Ge heterostructures
Applied Surface Science 115 Ž1997. 28–30
SiH 4 and GeH 4 chemical vapor deposition of GeSirGe heterostructures Shulin Gu ) , Xunming Zhu, Ning Jiang, Yi Shi, Rong Zhang, Youdou Zheng Department of Physics, Nanjing UniÕersity, Nanjing 210093, China Received 2 November 1995; accepted 7 October 1996
Abstract The deposition of GeSi alloys on Ge substrate by Rapid Thermal Process, Very Low Pressure CVD method has been studied. The growth rate of the GeSi alloy increases as the Si atoms are incorporated into the GeSi alloy at a proper temperature. The high substrate temperature will cause the Si fraction and the GeSi growth rate to increase.
1. Introduction The Si-rich SiGerSi heterostructure has made a great progress in material physics and device applications. Because of the limitation of the critical thickness, the Si-rich SiGe alloys can only be grown on Si substrates. However, the Ge-rich GeSi alloy has shown great potential applications on optic-electronic devices, such as GerGeSi quantum wells far infrared detectors w1x, high speed devices w2x. Recently, there began the study of Ge-rich GeSi alloys deposited on Ge substrates. GeSirGe heterostructures and quantum wells have been deposited by Molecular Beam Epitaxy ŽMBE. method w1,3x. There have been few reports on GeSi alloys deposited on Ge substrates by VLPCVD method. In the VLPCVD of SiH 4 and GeH 4 system, the growth condition of the SiGe alloys on the Si substrates is similar to that of Si epitaxy. High substrate temperatures Žabout 600–7008C. are neces-
)
Corresponding author. Fax: q86-25-3326028; e-mail: [email protected].
sary to decompose SiH 4 . However, the Ge epitaxy on Ge substrates must be carried out at low temperatures Žabout 350–4008C. for the low bonding energy of GeH, or three-dimensional island growth may happen. To deposit the Ge-rich GeSi on Ge substrates, we must decompose the small amount of SiH 4 gas molecules and not cause three-dimensional island growth. In this case, proper growth conditions such as the proper substrate temperature are the key factors. In this paper, we study the growth of GeSi alloys on Ge substrates by Rapid Thermal Process, Very Low Pressure CVD method. The experimental results of the growth rates and the compositions of the GeSi alloys could be understood on the basis of the surface controlled reaction of SiH 4 and GeH 4 .
2. Experiment details GeSi alloy samples were grown on GeŽ100. substrates by Rapid Thermal Process, Very Low Pressure CVD ŽRTPrVLP-CVD.. Details of the method
0169-4332r97r$17.00 Copyright q 1997 Elsevier Science B.V. All rights reserved. PII S 0 1 6 9 - 4 3 3 2 Ž 9 6 . 0 0 8 4 9 - 5
Shulin Gu et al.r Applied Surface Science 115 (1997) 28–30
have been reported elsewhere w4,5x. The growth substrate temperature was changed from 450 to 5508C. The GeH 4 flow rate was kept at 0.3 sccm, and the SiH 4 flow rate was changed from 0.04 to 0.25 sccm. The growth pressure was about 20 mTorr. We analyzed the GeSi alloys from Auger signals of Si ŽLVV, 92 eV. and Ge ŽLMM, 1147 eV. by Auger Electron Spectroscopy ŽPHI 550, ESCArSAM.. 1.5 KeV energy of Arq sputtering at the angle of 508 was used to get the AES depth profiles. A Standard Si 0.5 Ge 0.5 alloy Žfabricated by Si-MBE. has been referred to determine the atom compositions in the GeSi alloys.
3. Results and discussion To simplify growing process, we have deposited a series of multilayer samples with different concentration GeSi layers. During the sample deposition, the GeH 4 flow rate was kept at 0.28 sccm, and the SiH 4 flow rates were 0.04, 0.10, 0.15, 0.20, 0.25 sccm respectively, for different layers. Fig. 1 is an AES depth profile of a multilayer sample on the Ge substrate. The growth temperature was 4808C. Composition steps are observed obviously in the multilayer sample. As the SiH 4 flow rate is increased, Si fraction in the GeSi alloy increases linearly. The Si fractions in GeSi alloys against SiH 4 :GeH 4 flow ratio are shown in Fig. 2. The Si fractions are decided by the SiH 4 :GeH 4 flow ratios, and do not change as the GeH 4 flow rate increased. But, When the substrate temperature is increased, the Si fraction in the GeSi alloys increases at the same SiH 4 flow rate. Fig. 3
Fig. 1. AES depth profile of a multilayer sample deposited on Ge substrate, the growth temperature is 4808C.
29
Fig. 2. The Si fraction in the GeSi alloy against the SiH 4 :GeH 4 flow ratio at different GeH 4 flow rate.
shows, for the same SiH 4 :GeH 4 flow ratio, the Si composition is increased as the temperature is enhanced. From the AES depth profile, the GeSi growth rates were determined as a function of the SiH 4 flow rates as shown in Fig. 4. As the SiH 4 flow rate increases, the GeSi growth rate is enhanced. Fig. 5 shows the GeSi growth rates versus the substrate temperatures. The high temperature causes the GeSi growth rate to increase. The GeSi growth rate will vary with the SiH 4 flow rate. the GeSi growth rate against the SiH 4 flow rate at different substrate temperatures is shown in Fig. 5. At the high temperatures, the GeSi growth rate increases as SiH 4 flow rate is increased. At the low temperatures, however, the GeSi growth rate increases little or even decreases. The SiH 4 and GeH 4 VLPCVD of GeSi alloy on Ge substrate is a kind of surface controlled reaction
Fig. 3. The Si fraction in the GeSi alloy versus the SiH 4 :GeH 4 flow ratio at different substrate temperature.
30
Shulin Gu et al.r Applied Surface Science 115 (1997) 28–30
Fig. 4. The GeSi growth rate versus the SiH 4 flow rate.
w6,7x, which includes the reaction gases of SiH 4 and GeH 4 adsorption on and hydrogen desorption from the growing surface. Considering about the reaction constants, we find the GeH 4 adsorption rate will increase on GeSi surface than on pure Ge surface. But, the SiH 4 adsorption rate will decrease on the GeSi surface than on pure Si surface w6x. At the temperatures of the GeSi deposition region, the Si and Ge reaction rates Žgrowth rates. are controlled by hydrogen desorption step and GeH 4 adsorption step, respectively. So the GeH 4 adsorption rate will increase as the SiH 4 gas is added in. Fast hydrogen exchange between the Ge atom and the Si hydride on the growing surface will enhance hydrogen desorption rate from Si hydrides. Then, enough high temperature will make it possible for the Si atoms to be incorporated into the GeSi alloy when the SiH 4 gas can be decomposed into hydrides.
So as shown in Fig. 2 and Fig. 3, when the substrate temperature is increased, the Si fraction in the GeSi alloy will increase at a proper SiH 4 flow rate. Also, the GeSi growth rate will increase as the substrate temperature or the SiH 4 flow rate is increased, just as shown in Fig. 4 and Fig. 5. But, at the low temperatures, the SiH 4 gas molecules also adsorb on the growing surface but can not be decomposed into hydrides. in this case, the absorbed SiH 4 gas molecules become hinder centers for the adsorption of GeH 4 gas molecules, so the Ge growth rate will decrease and the Si atoms can not be incorporated into the growing layer. This can be understood from the change trend of the Si composition and the GeSi alloy growth rate against the substrate temperature in Fig. 3 and Fig. 4. In these two figures, the Si composition and the GeSi alloy growth rate are decreased as the substrate temperature is decreased. 4. Conclusion In conclusion, we have successfully deposited GeSi alloy on Ge substrate by Rapid Thermal Process, Very Low Pressure CVD method. A proper high temperature is important to grow the GeSi alloy. The GeSi growth rate increases as the Si atoms are incorporated into the GeSi alloy. The high substrate temperature will cause the Si fraction and the GeSi growth rate to increase. References
Fig. 5. The GeSi growth rate versus the substrate temperature.
w1x C. Lee and K.L. Wang, Appl. Phys. Lett. 64 Ž1994. 1256. w2x R. People, Phys. Rev. B 34 Ž1986. 2508. w3x K. Terashima, T. Ikarashi, D. Tweet, K. Mlyanaga, T. Tatsuml and M. Tajima, Appl. Phys. Lett. 65 Ž1994. 601. w4x Zheng Youdou, Zhang Rong, Hu Liqun, Jiang Ruolian, Zhong Peixin, Yu Shidong and Feng Duan, in: Proc. 20th Int. Conf. on Physics of Semiconductor, ed. E.M. Anastassakis and J.D. Joannopulos ŽWorld Scientific, Singapore, 1990. p. 869. w5x Zhang Rong, Zheng Youdou, Jiang Ruolian, Hu Liqun and Zhong Peixin, Appl. Surf. Sci. 48–49 Ž1991. 356. w6x N.M. Russell and W.G. Breiland, J. Appl. Phys. 73 Ž1993. 3525. w7x Shulin Gu, Youdou Zheng, Rong Zhang, Ronghua Wang and Peixin Zhong, J. Appl. Phys. 75 Ž1994. 5382.
SiH 4 and GeH 4 chemical vapor deposition of GeSirGe heterostructures Shulin Gu ) , Xunming Zhu, Ning Jiang, Yi Shi, Rong Zhang, Youdou Zheng Department of Physics, Nanjing UniÕersity, Nanjing 210093, China Received 2 November 1995; accepted 7 October 1996
Abstract The deposition of GeSi alloys on Ge substrate by Rapid Thermal Process, Very Low Pressure CVD method has been studied. The growth rate of the GeSi alloy increases as the Si atoms are incorporated into the GeSi alloy at a proper temperature. The high substrate temperature will cause the Si fraction and the GeSi growth rate to increase.
1. Introduction The Si-rich SiGerSi heterostructure has made a great progress in material physics and device applications. Because of the limitation of the critical thickness, the Si-rich SiGe alloys can only be grown on Si substrates. However, the Ge-rich GeSi alloy has shown great potential applications on optic-electronic devices, such as GerGeSi quantum wells far infrared detectors w1x, high speed devices w2x. Recently, there began the study of Ge-rich GeSi alloys deposited on Ge substrates. GeSirGe heterostructures and quantum wells have been deposited by Molecular Beam Epitaxy ŽMBE. method w1,3x. There have been few reports on GeSi alloys deposited on Ge substrates by VLPCVD method. In the VLPCVD of SiH 4 and GeH 4 system, the growth condition of the SiGe alloys on the Si substrates is similar to that of Si epitaxy. High substrate temperatures Žabout 600–7008C. are neces-
)
Corresponding author. Fax: q86-25-3326028; e-mail: [email protected].
sary to decompose SiH 4 . However, the Ge epitaxy on Ge substrates must be carried out at low temperatures Žabout 350–4008C. for the low bonding energy of GeH, or three-dimensional island growth may happen. To deposit the Ge-rich GeSi on Ge substrates, we must decompose the small amount of SiH 4 gas molecules and not cause three-dimensional island growth. In this case, proper growth conditions such as the proper substrate temperature are the key factors. In this paper, we study the growth of GeSi alloys on Ge substrates by Rapid Thermal Process, Very Low Pressure CVD method. The experimental results of the growth rates and the compositions of the GeSi alloys could be understood on the basis of the surface controlled reaction of SiH 4 and GeH 4 .
2. Experiment details GeSi alloy samples were grown on GeŽ100. substrates by Rapid Thermal Process, Very Low Pressure CVD ŽRTPrVLP-CVD.. Details of the method
0169-4332r97r$17.00 Copyright q 1997 Elsevier Science B.V. All rights reserved. PII S 0 1 6 9 - 4 3 3 2 Ž 9 6 . 0 0 8 4 9 - 5
Shulin Gu et al.r Applied Surface Science 115 (1997) 28–30
have been reported elsewhere w4,5x. The growth substrate temperature was changed from 450 to 5508C. The GeH 4 flow rate was kept at 0.3 sccm, and the SiH 4 flow rate was changed from 0.04 to 0.25 sccm. The growth pressure was about 20 mTorr. We analyzed the GeSi alloys from Auger signals of Si ŽLVV, 92 eV. and Ge ŽLMM, 1147 eV. by Auger Electron Spectroscopy ŽPHI 550, ESCArSAM.. 1.5 KeV energy of Arq sputtering at the angle of 508 was used to get the AES depth profiles. A Standard Si 0.5 Ge 0.5 alloy Žfabricated by Si-MBE. has been referred to determine the atom compositions in the GeSi alloys.
3. Results and discussion To simplify growing process, we have deposited a series of multilayer samples with different concentration GeSi layers. During the sample deposition, the GeH 4 flow rate was kept at 0.28 sccm, and the SiH 4 flow rates were 0.04, 0.10, 0.15, 0.20, 0.25 sccm respectively, for different layers. Fig. 1 is an AES depth profile of a multilayer sample on the Ge substrate. The growth temperature was 4808C. Composition steps are observed obviously in the multilayer sample. As the SiH 4 flow rate is increased, Si fraction in the GeSi alloy increases linearly. The Si fractions in GeSi alloys against SiH 4 :GeH 4 flow ratio are shown in Fig. 2. The Si fractions are decided by the SiH 4 :GeH 4 flow ratios, and do not change as the GeH 4 flow rate increased. But, When the substrate temperature is increased, the Si fraction in the GeSi alloys increases at the same SiH 4 flow rate. Fig. 3
Fig. 1. AES depth profile of a multilayer sample deposited on Ge substrate, the growth temperature is 4808C.
29
Fig. 2. The Si fraction in the GeSi alloy against the SiH 4 :GeH 4 flow ratio at different GeH 4 flow rate.
shows, for the same SiH 4 :GeH 4 flow ratio, the Si composition is increased as the temperature is enhanced. From the AES depth profile, the GeSi growth rates were determined as a function of the SiH 4 flow rates as shown in Fig. 4. As the SiH 4 flow rate increases, the GeSi growth rate is enhanced. Fig. 5 shows the GeSi growth rates versus the substrate temperatures. The high temperature causes the GeSi growth rate to increase. The GeSi growth rate will vary with the SiH 4 flow rate. the GeSi growth rate against the SiH 4 flow rate at different substrate temperatures is shown in Fig. 5. At the high temperatures, the GeSi growth rate increases as SiH 4 flow rate is increased. At the low temperatures, however, the GeSi growth rate increases little or even decreases. The SiH 4 and GeH 4 VLPCVD of GeSi alloy on Ge substrate is a kind of surface controlled reaction
Fig. 3. The Si fraction in the GeSi alloy versus the SiH 4 :GeH 4 flow ratio at different substrate temperature.
30
Shulin Gu et al.r Applied Surface Science 115 (1997) 28–30
Fig. 4. The GeSi growth rate versus the SiH 4 flow rate.
w6,7x, which includes the reaction gases of SiH 4 and GeH 4 adsorption on and hydrogen desorption from the growing surface. Considering about the reaction constants, we find the GeH 4 adsorption rate will increase on GeSi surface than on pure Ge surface. But, the SiH 4 adsorption rate will decrease on the GeSi surface than on pure Si surface w6x. At the temperatures of the GeSi deposition region, the Si and Ge reaction rates Žgrowth rates. are controlled by hydrogen desorption step and GeH 4 adsorption step, respectively. So the GeH 4 adsorption rate will increase as the SiH 4 gas is added in. Fast hydrogen exchange between the Ge atom and the Si hydride on the growing surface will enhance hydrogen desorption rate from Si hydrides. Then, enough high temperature will make it possible for the Si atoms to be incorporated into the GeSi alloy when the SiH 4 gas can be decomposed into hydrides.
So as shown in Fig. 2 and Fig. 3, when the substrate temperature is increased, the Si fraction in the GeSi alloy will increase at a proper SiH 4 flow rate. Also, the GeSi growth rate will increase as the substrate temperature or the SiH 4 flow rate is increased, just as shown in Fig. 4 and Fig. 5. But, at the low temperatures, the SiH 4 gas molecules also adsorb on the growing surface but can not be decomposed into hydrides. in this case, the absorbed SiH 4 gas molecules become hinder centers for the adsorption of GeH 4 gas molecules, so the Ge growth rate will decrease and the Si atoms can not be incorporated into the growing layer. This can be understood from the change trend of the Si composition and the GeSi alloy growth rate against the substrate temperature in Fig. 3 and Fig. 4. In these two figures, the Si composition and the GeSi alloy growth rate are decreased as the substrate temperature is decreased. 4. Conclusion In conclusion, we have successfully deposited GeSi alloy on Ge substrate by Rapid Thermal Process, Very Low Pressure CVD method. A proper high temperature is important to grow the GeSi alloy. The GeSi growth rate increases as the Si atoms are incorporated into the GeSi alloy. The high substrate temperature will cause the Si fraction and the GeSi growth rate to increase. References
Fig. 5. The GeSi growth rate versus the substrate temperature.
w1x C. Lee and K.L. Wang, Appl. Phys. Lett. 64 Ž1994. 1256. w2x R. People, Phys. Rev. B 34 Ž1986. 2508. w3x K. Terashima, T. Ikarashi, D. Tweet, K. Mlyanaga, T. Tatsuml and M. Tajima, Appl. Phys. Lett. 65 Ž1994. 601. w4x Zheng Youdou, Zhang Rong, Hu Liqun, Jiang Ruolian, Zhong Peixin, Yu Shidong and Feng Duan, in: Proc. 20th Int. Conf. on Physics of Semiconductor, ed. E.M. Anastassakis and J.D. Joannopulos ŽWorld Scientific, Singapore, 1990. p. 869. w5x Zhang Rong, Zheng Youdou, Jiang Ruolian, Hu Liqun and Zhong Peixin, Appl. Surf. Sci. 48–49 Ž1991. 356. w6x N.M. Russell and W.G. Breiland, J. Appl. Phys. 73 Ž1993. 3525. w7x Shulin Gu, Youdou Zheng, Rong Zhang, Ronghua Wang and Peixin Zhong, J. Appl. Phys. 75 Ž1994. 5382.