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InAsPSb heterostructures
Applied Surface Science 244 (2005) 297–300 www.elsevier.com/locate/apsusc
Influence of Si3N4 and ZnS films on transmittance of InAsSb/InAsPSb heterostructures Y.Z. Gaoa,*, X.Y. Gonga, W.Z. Fangb, H.Y. Dengb, G.J. Hub, M. Aoyamac, T. Yamaguchic, N. Daib a
Institute of Semiconductor and Information Technology, TongJi University, 1239 Siping Road, Shanghai 200092, China b National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 420 Zhong Shan Bei Yi Road, Shanghai 200083, China c Research Institute of Electronics, Shizuoka University, Hamamatsu 432-8011, Japan Received 9 June 2004; accepted 8 October 2004 Available online 8 January 2005
Abstract The transmittance of InAsSb/InAsPSb heterostructures is remarkably improved by depositing a Si3N4 top layer. This demonstrates its good anti-reflective property. A study of the influence of various factors on the transmittance of the heterostructures is performed. A comparison was made between the transmittances of the heterostructures under different conditions. The different effects of Si3N4 and ZnS top layers on the transmittance of the InAsSb/InAsPSb heterostructures are discussed. # 2004 Published by Elsevier B.V. PACS: 68. 47. Fg Keywords: InAsSb/InAsPSb; FTIR; Si3N4; ZnS; Deposition; Transmittance
1. Introduction The InAsSb/InAsPSb heterostructures are important material for room temperature photodetectors and light emitting diodes (LED) in 3–5 mm wavelength range. Such kind devices have extensive applications in trace * Corresponding author. Tel.: +86 21 65981457; fax: +86 21 65980862. E-mail address: [email protected] (Y.Z. Gao). 0169-4332/$ – see front matter # 2004 Published by Elsevier B.V. doi:10.1016/j.apsusc.2004.10.123
monitoring, common pollutant analysis, ultra-low optical fiber communications and so on [1]. To improve the performance of the photo-devices, surface passivation is a very important process due to the existence of high-density surface states, which have a drastic effect on the dark current of the devices [2,3]. On the other hand, decreasing the reflection and the absorption loss in the top layer, i.e., increasing the transmittance of the heterostructures has also very significant effect on the performance of the photodevices [4,5].
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Y.Z. Gao et al. / Applied Surface Science 244 (2005) 297–300
In this study, the influences of Si3N4 and ZnS top layers, which were chosen as anti-reflective layers due to their suitable refractive index and energy ban gap, on the transmittance of the InAsPSb/InAsSb were clarified. A comparison was made between the transmittances of the heterostructures to check the effect of top layers and Zn doping amount, which is inevitable for p–n junction type photo-devices. The superior anti-reflective property of Si3N4 was demonstrated though its thickness of 700 nm is not an optimized value.
2. Experimental The InAsSb/InAsPSb multi-layers were grown in a liquid phase epitaxy (LPE) growth system using a multi-well sliding graphite boat on (1 0 0)InAs substrates between 530 and 500˚ C. High purity (7N) In, Sb, non-doped InAs and InP polycrystalline were used as the source materials. The Zn was employed as a p-type dopant for the p-InAsPSb layer growth. To check the structural quality of the epilayers, Xray diffraction (XRD) measurements were carried out on an InAs/InAsPSb layer using a Philips X’pert materials research diffractometer. The measurements were performed under a voltage of 35 kV and a current of 30 mA. The scan mode is 2u/v in the range of 25– 85˚ . To study the influence of top layers on the transmittance of the InAsSb/InAsPSb, a 513 nm (actually 700 nm) thick Si3N4 and a 466 mm thick ZnS films were designed according to the relation between their refractive indexes and the wavelength of around 4.1 mm for the heterostructures, then were deposited on the surfaces of the InAsPSb layers, respectively, by PECVD and by thermal evaporation. The transmittances of the InAsSb/InAsPSb heterostructures were measured using a NEXUS 670 FTIR spectrophotometer with a resolution of 1.928 cm 1. The measurements were performed on the heterostructures under different conditions including with and without an InAsPSb layer, with and without Zndoping in the InAsPSb layers; before and after deposition of an anti-reflective layers on the surface of the InAsPSb layers.
3. Results and discussions 3.1. X-ray diffraction measurements To check the structural quality of the epilayers, Xray diffraction measurements were carried out. In Fig. 1, the X-ray diffraction spectra for an InAs/ InAsPSb hetero-epilayer are shown. The (4 0 0) and (2 0 0) diffraction peaks Cu Ka from the InAsPSb epilayer and from the InAs substrate, respectively, are seen from the figure. Besides, the very weak (4 0 0) Cu Kb peaks from the layer and from the substrate, and the weak (2 0 0) Cu Kb peak from the layer are also appeared, which may be caused by the selective absorption of the thin Ni filter involved in XRD analyzer. No other peak can be found in 2u range indicating good single crystal structure of the epilayer. In order to know the structure of the strong (4 0 0) Cu Ka peaks, the amplified corresponding peaks are shown in the inset of Fig. 1. The diffraction peaks of Cu Ka1 and Cu Ka2 from the InAsPSb epilayer and from the InAs substrate, respectively, can be clearly seen in the insert. The (4 0 0) Cu Ka1 peak from the epilayer is very sharp and symmetric. The full width at half maximum (FWHM) of this peak is nearly 130 arcsec indicating high quality of the epilayer.
Fig. 1. X-ray diffraction spectra for an InAs/InAsPSb heterostructure. The inset shows the amplification of the main peak.
Y.Z. Gao et al. / Applied Surface Science 244 (2005) 297–300
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Fig. 2. Transmission spectra for the four InAsSb/InAsPSb heterostructures under different conditions.
Fig. 3. Transmission spectra for the InAsSb/InAsPSb sample TY-3 before (a) and after (b) deposition of 470 nm ZnS top layers.
3.2. Transmittance of InAsSb/InAsPSb heterostructures
is also observed for the two samples due to the same reason as samples TY-1 and TY-2. It is also seen from Fig. 2 that the absorption edges appear at around 2500 cm 1 for all the samples and are very sharp indicating good quality of the epilayers.
To study the influence of various factors on the transmittance of the heterostructures, transmission measurements were performed for four InAsSb/ InAsPSb samples. In Fig. 2, the transmission spectra at 300 K are shown. It is seen that the transmittances of the samples are successively decreased. The sample TY-1 is a n1-InAsSb/n2-InAsSb double-layer grown on the n-InAs substrate, which has highest transmittance. TY-2 has the same structure as that of TY-1, but a nondoped n-InAs0.80P0.12Sb0.08 wide gap layer with an energy gap of 0.41 eV (3311 cm 1) was grown on the surface of n2-InAsSb layer. It is seen that the transmittance of this sample is decreased about 7.8% comparing with that of TY-1. This is reasonable and indicating a good window action of the InAsPSb wide gap top layer. The decrease of transmittances at wavenumbers larger than 500 cm 1 may be related to scattered reflection of rough back surfaces of the substrates. The samples TY-3 and TY-4 have same structure as that of sample TY-2. However, 3.47 10 4 and 5.46 10 4 at.% Zn were, respectively, added in the growth melts for InAsPSb layers. The transmittances of the two samples are evidently decreased. This is caused by free carrier absorption in the Zn-doped pInAsPSb layers. The transmittance of TY-4 is a little lower than that of the sample TY-3 due to its higher Zn-doping level. This result indicates that the Zn doping and its amount directly affect on the shape of transmission spectra of the samples. The decrease of transmittances at wavenumbers larger than 500 cm 1
3.3. Influence of Si3N4 and ZnS thin films on the transmittance of InAsSb/InAsPSb In order to search a suitable anti-reflective film, the influence of Si3N4 and ZnS top layers on the transmittance of the heterostructures are investigated. In Fig. 3, the transmission spectra for the sample TY-3 before (a) and after (b) the deposition of a ZnS film are shown. It is seen that the transmittance of the sample (b) is decreased about 25% after the deposition of a ZnS thin film. This result is surprising because the thickness of 470 nm is nearly optimized, and was designed to get highest anti-reflective effect at 2418 cm 1. In the spectra of the both samples, a decrease of the transmittances at the wavenumbers of around 2400 cm 1 can be seen. This comes from the free carrier absorption in the Zn-doped p-InAsPSb top layer. Fig. 4 shows the transmission spectra for the sample TY-4 before (a) and after (b) the deposition of a Si3N4 film. It is seen that after the deposition of Si3N4 film, the transmittance is remarkably increased (about 17%) though the real thickness of 700 nm is deviated from designed value of 513 nm. The absorption edges for the two samples all are appeared at about 2400 cm 1 as seen from the figure. For sample TY-4 (b), a large drop of the transmittance is
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Y.Z. Gao et al. / Applied Surface Science 244 (2005) 297–300
Zn doping in the InAsPSb layer evidently decrease the transmittance due to the free carrier absorption. The transmittance of the heterostructures is improved again after the deposition of a Si3N4 top layer on the surface of the InAsPSb layer indicating its good antireflective property.
Acknowledgement Fig. 4. Transmission spectra for the InAsSb/InAsPSb sample TY-4 before (a) and after (b) deposition of 700 nm Si3N4 top layers.
observed at a wavenumber of around 900 cm 1. It comes from water absorption existed in the deposition system for Si3N4 top layers.
This work is financially supported by National natural scientific fund under Contract Nos. 60376002 and 56276036.
References 4. Summary The InAsSb/InAsPSb heterostructures were grown by the LPE technique. X-ray diffraction measurements showed a good structure quality of the heterostructures. A study of the influence of various factors on the transmittance of heterostructures showed that after the deposition of a wide gap InAsPSb layer the transmittance of the InAsSb layers is only decreased about 7.8% indicating the window action of this layer.
[1] S. Kim, M. Erdtmann, D. Wu, E. Kass, H. Yi, J. Diaz, M. Razeghi, Appl. Phys. Lett. 69 (1996) 1614. [2] X.Y. Gong, T. Yamaguchi, H. Kan, T. Makino, T. Iida, T. Kato, M. Aoyama, Y. Suzuki, N. Sanada, Y. Fukuda, M. Kumagawa, Jpn. J. Appl. Phys. 37 (1998) 55. [3] X.Y. Gong, H. Kan, T. Makino, T. Iida, Y.Z. Gao, M. Aoyama, M. Kumagawa, T. Yamaguchi, Jpn. J. Appl. Phys. 38 (1999) 685. [4] A. Smakula, J. Kalnajs, M.J. Redman, Appl. Opt. 3 (1964) 323. [5] G.J. Van der Kolk, T. Trinh, W. fleischer, M. Griepentrog, in: Proceedings of the 41st SVC Technical Conference, 1998, p. 44.
Influence of Si3N4 and ZnS films on transmittance of InAsSb/InAsPSb heterostructures Y.Z. Gaoa,*, X.Y. Gonga, W.Z. Fangb, H.Y. Dengb, G.J. Hub, M. Aoyamac, T. Yamaguchic, N. Daib a
Institute of Semiconductor and Information Technology, TongJi University, 1239 Siping Road, Shanghai 200092, China b National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 420 Zhong Shan Bei Yi Road, Shanghai 200083, China c Research Institute of Electronics, Shizuoka University, Hamamatsu 432-8011, Japan Received 9 June 2004; accepted 8 October 2004 Available online 8 January 2005
Abstract The transmittance of InAsSb/InAsPSb heterostructures is remarkably improved by depositing a Si3N4 top layer. This demonstrates its good anti-reflective property. A study of the influence of various factors on the transmittance of the heterostructures is performed. A comparison was made between the transmittances of the heterostructures under different conditions. The different effects of Si3N4 and ZnS top layers on the transmittance of the InAsSb/InAsPSb heterostructures are discussed. # 2004 Published by Elsevier B.V. PACS: 68. 47. Fg Keywords: InAsSb/InAsPSb; FTIR; Si3N4; ZnS; Deposition; Transmittance
1. Introduction The InAsSb/InAsPSb heterostructures are important material for room temperature photodetectors and light emitting diodes (LED) in 3–5 mm wavelength range. Such kind devices have extensive applications in trace * Corresponding author. Tel.: +86 21 65981457; fax: +86 21 65980862. E-mail address: [email protected] (Y.Z. Gao). 0169-4332/$ – see front matter # 2004 Published by Elsevier B.V. doi:10.1016/j.apsusc.2004.10.123
monitoring, common pollutant analysis, ultra-low optical fiber communications and so on [1]. To improve the performance of the photo-devices, surface passivation is a very important process due to the existence of high-density surface states, which have a drastic effect on the dark current of the devices [2,3]. On the other hand, decreasing the reflection and the absorption loss in the top layer, i.e., increasing the transmittance of the heterostructures has also very significant effect on the performance of the photodevices [4,5].
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Y.Z. Gao et al. / Applied Surface Science 244 (2005) 297–300
In this study, the influences of Si3N4 and ZnS top layers, which were chosen as anti-reflective layers due to their suitable refractive index and energy ban gap, on the transmittance of the InAsPSb/InAsSb were clarified. A comparison was made between the transmittances of the heterostructures to check the effect of top layers and Zn doping amount, which is inevitable for p–n junction type photo-devices. The superior anti-reflective property of Si3N4 was demonstrated though its thickness of 700 nm is not an optimized value.
2. Experimental The InAsSb/InAsPSb multi-layers were grown in a liquid phase epitaxy (LPE) growth system using a multi-well sliding graphite boat on (1 0 0)InAs substrates between 530 and 500˚ C. High purity (7N) In, Sb, non-doped InAs and InP polycrystalline were used as the source materials. The Zn was employed as a p-type dopant for the p-InAsPSb layer growth. To check the structural quality of the epilayers, Xray diffraction (XRD) measurements were carried out on an InAs/InAsPSb layer using a Philips X’pert materials research diffractometer. The measurements were performed under a voltage of 35 kV and a current of 30 mA. The scan mode is 2u/v in the range of 25– 85˚ . To study the influence of top layers on the transmittance of the InAsSb/InAsPSb, a 513 nm (actually 700 nm) thick Si3N4 and a 466 mm thick ZnS films were designed according to the relation between their refractive indexes and the wavelength of around 4.1 mm for the heterostructures, then were deposited on the surfaces of the InAsPSb layers, respectively, by PECVD and by thermal evaporation. The transmittances of the InAsSb/InAsPSb heterostructures were measured using a NEXUS 670 FTIR spectrophotometer with a resolution of 1.928 cm 1. The measurements were performed on the heterostructures under different conditions including with and without an InAsPSb layer, with and without Zndoping in the InAsPSb layers; before and after deposition of an anti-reflective layers on the surface of the InAsPSb layers.
3. Results and discussions 3.1. X-ray diffraction measurements To check the structural quality of the epilayers, Xray diffraction measurements were carried out. In Fig. 1, the X-ray diffraction spectra for an InAs/ InAsPSb hetero-epilayer are shown. The (4 0 0) and (2 0 0) diffraction peaks Cu Ka from the InAsPSb epilayer and from the InAs substrate, respectively, are seen from the figure. Besides, the very weak (4 0 0) Cu Kb peaks from the layer and from the substrate, and the weak (2 0 0) Cu Kb peak from the layer are also appeared, which may be caused by the selective absorption of the thin Ni filter involved in XRD analyzer. No other peak can be found in 2u range indicating good single crystal structure of the epilayer. In order to know the structure of the strong (4 0 0) Cu Ka peaks, the amplified corresponding peaks are shown in the inset of Fig. 1. The diffraction peaks of Cu Ka1 and Cu Ka2 from the InAsPSb epilayer and from the InAs substrate, respectively, can be clearly seen in the insert. The (4 0 0) Cu Ka1 peak from the epilayer is very sharp and symmetric. The full width at half maximum (FWHM) of this peak is nearly 130 arcsec indicating high quality of the epilayer.
Fig. 1. X-ray diffraction spectra for an InAs/InAsPSb heterostructure. The inset shows the amplification of the main peak.
Y.Z. Gao et al. / Applied Surface Science 244 (2005) 297–300
299
Fig. 2. Transmission spectra for the four InAsSb/InAsPSb heterostructures under different conditions.
Fig. 3. Transmission spectra for the InAsSb/InAsPSb sample TY-3 before (a) and after (b) deposition of 470 nm ZnS top layers.
3.2. Transmittance of InAsSb/InAsPSb heterostructures
is also observed for the two samples due to the same reason as samples TY-1 and TY-2. It is also seen from Fig. 2 that the absorption edges appear at around 2500 cm 1 for all the samples and are very sharp indicating good quality of the epilayers.
To study the influence of various factors on the transmittance of the heterostructures, transmission measurements were performed for four InAsSb/ InAsPSb samples. In Fig. 2, the transmission spectra at 300 K are shown. It is seen that the transmittances of the samples are successively decreased. The sample TY-1 is a n1-InAsSb/n2-InAsSb double-layer grown on the n-InAs substrate, which has highest transmittance. TY-2 has the same structure as that of TY-1, but a nondoped n-InAs0.80P0.12Sb0.08 wide gap layer with an energy gap of 0.41 eV (3311 cm 1) was grown on the surface of n2-InAsSb layer. It is seen that the transmittance of this sample is decreased about 7.8% comparing with that of TY-1. This is reasonable and indicating a good window action of the InAsPSb wide gap top layer. The decrease of transmittances at wavenumbers larger than 500 cm 1 may be related to scattered reflection of rough back surfaces of the substrates. The samples TY-3 and TY-4 have same structure as that of sample TY-2. However, 3.47 10 4 and 5.46 10 4 at.% Zn were, respectively, added in the growth melts for InAsPSb layers. The transmittances of the two samples are evidently decreased. This is caused by free carrier absorption in the Zn-doped pInAsPSb layers. The transmittance of TY-4 is a little lower than that of the sample TY-3 due to its higher Zn-doping level. This result indicates that the Zn doping and its amount directly affect on the shape of transmission spectra of the samples. The decrease of transmittances at wavenumbers larger than 500 cm 1
3.3. Influence of Si3N4 and ZnS thin films on the transmittance of InAsSb/InAsPSb In order to search a suitable anti-reflective film, the influence of Si3N4 and ZnS top layers on the transmittance of the heterostructures are investigated. In Fig. 3, the transmission spectra for the sample TY-3 before (a) and after (b) the deposition of a ZnS film are shown. It is seen that the transmittance of the sample (b) is decreased about 25% after the deposition of a ZnS thin film. This result is surprising because the thickness of 470 nm is nearly optimized, and was designed to get highest anti-reflective effect at 2418 cm 1. In the spectra of the both samples, a decrease of the transmittances at the wavenumbers of around 2400 cm 1 can be seen. This comes from the free carrier absorption in the Zn-doped p-InAsPSb top layer. Fig. 4 shows the transmission spectra for the sample TY-4 before (a) and after (b) the deposition of a Si3N4 film. It is seen that after the deposition of Si3N4 film, the transmittance is remarkably increased (about 17%) though the real thickness of 700 nm is deviated from designed value of 513 nm. The absorption edges for the two samples all are appeared at about 2400 cm 1 as seen from the figure. For sample TY-4 (b), a large drop of the transmittance is
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Y.Z. Gao et al. / Applied Surface Science 244 (2005) 297–300
Zn doping in the InAsPSb layer evidently decrease the transmittance due to the free carrier absorption. The transmittance of the heterostructures is improved again after the deposition of a Si3N4 top layer on the surface of the InAsPSb layer indicating its good antireflective property.
Acknowledgement Fig. 4. Transmission spectra for the InAsSb/InAsPSb sample TY-4 before (a) and after (b) deposition of 700 nm Si3N4 top layers.
observed at a wavenumber of around 900 cm 1. It comes from water absorption existed in the deposition system for Si3N4 top layers.
This work is financially supported by National natural scientific fund under Contract Nos. 60376002 and 56276036.
References 4. Summary The InAsSb/InAsPSb heterostructures were grown by the LPE technique. X-ray diffraction measurements showed a good structure quality of the heterostructures. A study of the influence of various factors on the transmittance of heterostructures showed that after the deposition of a wide gap InAsPSb layer the transmittance of the InAsSb layers is only decreased about 7.8% indicating the window action of this layer.
[1] S. Kim, M. Erdtmann, D. Wu, E. Kass, H. Yi, J. Diaz, M. Razeghi, Appl. Phys. Lett. 69 (1996) 1614. [2] X.Y. Gong, T. Yamaguchi, H. Kan, T. Makino, T. Iida, T. Kato, M. Aoyama, Y. Suzuki, N. Sanada, Y. Fukuda, M. Kumagawa, Jpn. J. Appl. Phys. 37 (1998) 55. [3] X.Y. Gong, H. Kan, T. Makino, T. Iida, Y.Z. Gao, M. Aoyama, M. Kumagawa, T. Yamaguchi, Jpn. J. Appl. Phys. 38 (1999) 685. [4] A. Smakula, J. Kalnajs, M.J. Redman, Appl. Opt. 3 (1964) 323. [5] G.J. Van der Kolk, T. Trinh, W. fleischer, M. Griepentrog, in: Proceedings of the 41st SVC Technical Conference, 1998, p. 44.