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GaAs superlattice for negative-differential-resistance transistor
Abstracts
Effect of parameter variation on the performance of InGaAsP/InP multiple-quantum-well electroabsorption/electrorefraction modulators F K Xiong, L D Zhu and C W Wang, Institute of Semiconductors,
Academia Sinica, Belling 100083, China The dependence of electroabsorption and electrorefraction in In1 xGaxAsyPl_y/InP multiple-quantum-well (MQW) structure on the M Q W parameter (as P mole fraction y, well thickness L~, residual impurity concentration Ndl in i region and interface quality) and on the applied electric field is investigated theoretically. The relationship between the performance of a MQW long-wavelength phase modulator and electrorefraction is also investigated. A factor An/a is introduced in order to characterize the performance of the phase modulator more perfectly. Large An/a means high modulation efficiency and low insertion loss. Our theoretical study shows that the Inl_xGaxAsyPl_y/InP M Q W structure with y = 0.9, Lz = 100/~, Ndi = 1 X 1015 cm -3 is appropriate for a phase modulator. The factor An/a of the structure is predicted to increase by a factor of about 1 × 103 in the wavelength range of 1.5-1.55 m, compared with that of the structure with y = 1, L~ = 60/~, Ndi 1 x l 015 c m - 3. High interface quality and low i region residual impurity concentration are in favor of the fast and efficient M Q W modulators. =
Application of AIGaAs/GaAs superlattice for negative-differentialresistance transistor W C Lin, W S Lour, C Y Sun, Y S Lee and D F Gno, Department
of Electrical Engineering, Chang-Kung University, 1 University Road, Tainan, Taiwan, China 1. Introduction Pioneering work on resonant-tunnelling through a heterostructure quantum well was first done by Tsu, Esaki and Chang et al though the observed negative-differential-resistance effects were too small to be useful in device applications. Recently, the remarkable progress in MBE made possible the observation of high peak-to-valley ratios in resonant-tunnelling double barriers. In this presentation, a novel resonant-tunnelling bipolar transistor employing an i-A1GaAs/GaAs superlattice as a resonant-tunnelling emitter will be discussed. It is found that the transistor studied exhibits not only high current gain but significant double negative-differential-resistance. 2. Experiment The proposed structure grown by MBE includes the resonanttunnelling superlattice emitter, the 50 A A1GaAs barriers which are undoped, while the 50 A GaAs wells are heavily doped with Si to 1 x 1018 cm 3. After epitaxial growth, the device fabrication was fulfilled by using a conventional evaporation process and lift-off technique. 3. Discussion In order to understand the physics of the structure, the corresponding energy bands have to be considered. The collectoremitter bias is fixed and the input base current is increased successively. At low values of IB i.e. small VBE, the applied VBE is 1078
essentially across the E-B junction until the flat-band condition is achieved. Within this region, the device behaves as a conventional bipolar transistor. Increasing IB (VBE) beyond the flat-band condition, causes the excess applied voltage to appear across the superlattice. At some critical value Ithl, the Fermi-level then elevates beyond the ground band E j of the superlattice. This causes firstly an abrupt drop in collector current and sudden quenching of the current gain. Similarly, the on and off resonanttunnelling through E2 occurs at Ith2. Obviously, there are three different operating regimes of transistor action and double negative-differential-resistance region, as described above. 4. Conclusion A novel superlattice-emitter transistor with double negativedifferential-resistance has been fabricated successfully. Due to the significantly high performace, it is attractive to exploit the studied device in multiple-valued circuits and frequency multipliers.
Characterization of GaAs thin films grown by molecular beam epitaxy on Si-on-insulator Zhu Wenhua, Lin Chenglu, Yu Yuehui, Li Aizhen and Zou Shichang, Ion Beam Laboratory, Shanghai Institute of Metallurgy, Academia Sinica, Shanghai 200050, China; and P L F Hemment, Department of Electronic and Electrical Engineering,
University of Surrey, Guildford, Surrey GU2 5HX, UK Silicon-on-insulator (SOI) structures have excellent potential in high speed and radiation hardened LSI devices. The epitaxial growth of GaAs on the SO1 substrate would result in heteroepitaxial wafers with all the advantages of GaAs on Si and SOI. This paper reports the first demonstration of undoped GaAs thin films on SOI by Molecular Beam Epitaxy (MBE). The SO1 substrates were prepared using the Separation by IMplantation of OXygen (SIMOX) process. Rutherford backscattering and channeling (RBS/C), and infrared (ir) reflection measurements have been employed to characterize the GaAs thin films. RBS/C results show that there is considerable lattice disorder at the GaAs-Si interface, although the crystal quality of GaAs thin films improves remarkably towards the GaAs surface for thicker films where the minimum channeling yield drops to 10%. ir reflection spectra in the wavenumber range of 1500-5000 cm J were measured for GaAs thin films on SIMOX. Interference fringes observed in ir reflection spectra also prove that the crystalline GaAs thin films have been deposited on SO1 substrates. By computer simulation of ir reflection interference spectra, refractive index profiles of the GaAs/SIMOX structures were obtained.
Poly-Si film and its application in the pressure sensors Gao Qi'an and Xu Yingru, Department of Applied Physics, Hefei
University of Technology, Hefei 230009, Anhui, China The Poly-Si film pressure sensor will be used widely due to its good high-temperature properties, high sensitivity, reliability and cheapness. Good-quality poly-Si film pressure sensors depend on
Effect of parameter variation on the performance of InGaAsP/InP multiple-quantum-well electroabsorption/electrorefraction modulators F K Xiong, L D Zhu and C W Wang, Institute of Semiconductors,
Academia Sinica, Belling 100083, China The dependence of electroabsorption and electrorefraction in In1 xGaxAsyPl_y/InP multiple-quantum-well (MQW) structure on the M Q W parameter (as P mole fraction y, well thickness L~, residual impurity concentration Ndl in i region and interface quality) and on the applied electric field is investigated theoretically. The relationship between the performance of a MQW long-wavelength phase modulator and electrorefraction is also investigated. A factor An/a is introduced in order to characterize the performance of the phase modulator more perfectly. Large An/a means high modulation efficiency and low insertion loss. Our theoretical study shows that the Inl_xGaxAsyPl_y/InP M Q W structure with y = 0.9, Lz = 100/~, Ndi = 1 X 1015 cm -3 is appropriate for a phase modulator. The factor An/a of the structure is predicted to increase by a factor of about 1 × 103 in the wavelength range of 1.5-1.55 m, compared with that of the structure with y = 1, L~ = 60/~, Ndi 1 x l 015 c m - 3. High interface quality and low i region residual impurity concentration are in favor of the fast and efficient M Q W modulators. =
Application of AIGaAs/GaAs superlattice for negative-differentialresistance transistor W C Lin, W S Lour, C Y Sun, Y S Lee and D F Gno, Department
of Electrical Engineering, Chang-Kung University, 1 University Road, Tainan, Taiwan, China 1. Introduction Pioneering work on resonant-tunnelling through a heterostructure quantum well was first done by Tsu, Esaki and Chang et al though the observed negative-differential-resistance effects were too small to be useful in device applications. Recently, the remarkable progress in MBE made possible the observation of high peak-to-valley ratios in resonant-tunnelling double barriers. In this presentation, a novel resonant-tunnelling bipolar transistor employing an i-A1GaAs/GaAs superlattice as a resonant-tunnelling emitter will be discussed. It is found that the transistor studied exhibits not only high current gain but significant double negative-differential-resistance. 2. Experiment The proposed structure grown by MBE includes the resonanttunnelling superlattice emitter, the 50 A A1GaAs barriers which are undoped, while the 50 A GaAs wells are heavily doped with Si to 1 x 1018 cm 3. After epitaxial growth, the device fabrication was fulfilled by using a conventional evaporation process and lift-off technique. 3. Discussion In order to understand the physics of the structure, the corresponding energy bands have to be considered. The collectoremitter bias is fixed and the input base current is increased successively. At low values of IB i.e. small VBE, the applied VBE is 1078
essentially across the E-B junction until the flat-band condition is achieved. Within this region, the device behaves as a conventional bipolar transistor. Increasing IB (VBE) beyond the flat-band condition, causes the excess applied voltage to appear across the superlattice. At some critical value Ithl, the Fermi-level then elevates beyond the ground band E j of the superlattice. This causes firstly an abrupt drop in collector current and sudden quenching of the current gain. Similarly, the on and off resonanttunnelling through E2 occurs at Ith2. Obviously, there are three different operating regimes of transistor action and double negative-differential-resistance region, as described above. 4. Conclusion A novel superlattice-emitter transistor with double negativedifferential-resistance has been fabricated successfully. Due to the significantly high performace, it is attractive to exploit the studied device in multiple-valued circuits and frequency multipliers.
Characterization of GaAs thin films grown by molecular beam epitaxy on Si-on-insulator Zhu Wenhua, Lin Chenglu, Yu Yuehui, Li Aizhen and Zou Shichang, Ion Beam Laboratory, Shanghai Institute of Metallurgy, Academia Sinica, Shanghai 200050, China; and P L F Hemment, Department of Electronic and Electrical Engineering,
University of Surrey, Guildford, Surrey GU2 5HX, UK Silicon-on-insulator (SOI) structures have excellent potential in high speed and radiation hardened LSI devices. The epitaxial growth of GaAs on the SO1 substrate would result in heteroepitaxial wafers with all the advantages of GaAs on Si and SOI. This paper reports the first demonstration of undoped GaAs thin films on SOI by Molecular Beam Epitaxy (MBE). The SO1 substrates were prepared using the Separation by IMplantation of OXygen (SIMOX) process. Rutherford backscattering and channeling (RBS/C), and infrared (ir) reflection measurements have been employed to characterize the GaAs thin films. RBS/C results show that there is considerable lattice disorder at the GaAs-Si interface, although the crystal quality of GaAs thin films improves remarkably towards the GaAs surface for thicker films where the minimum channeling yield drops to 10%. ir reflection spectra in the wavenumber range of 1500-5000 cm J were measured for GaAs thin films on SIMOX. Interference fringes observed in ir reflection spectra also prove that the crystalline GaAs thin films have been deposited on SO1 substrates. By computer simulation of ir reflection interference spectra, refractive index profiles of the GaAs/SIMOX structures were obtained.
Poly-Si film and its application in the pressure sensors Gao Qi'an and Xu Yingru, Department of Applied Physics, Hefei
University of Technology, Hefei 230009, Anhui, China The Poly-Si film pressure sensor will be used widely due to its good high-temperature properties, high sensitivity, reliability and cheapness. Good-quality poly-Si film pressure sensors depend on