Study of Medium-Deep Traps in Undoped GaAs Grown by Arsenic-Pressure Controlled CZ Method
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STUDY OF MEDIUM-DEEP TRAPS IN UNDOPED GaAs GROWN BY ARSENIC-PRESSURE CONTROLLED CZ METHOD
Hiroyuki Shiraki, Yutaka Tokuda*, and Koichi Sassa** Central Research Institute, Mitsubishi Materials Corporation, 1-297 Kitabukuro-cho, Omiya, Saitama, Japan * Department of Electronics, Aichi Institute of Technology, 1247 Yachigusa Yakusa-cho, Toyota, Aichi, Japan **Compound Semiconductor Center, Mitsubishi Materials Corporation, 1-297 Kitabukuro-cho, Omiya, Saitama, Japan
ABSTRACT Properties of medium-deep traps in n-type undoped GaAs crystals grown by arsenic-pressure controlled Czochralski (PCZ) method were studied by using capacitance transient spectroscopy (CTS) and temperature-dependent Hall (TDH) measurement. EL3 and EL6-like (EM2) traps were dominant medium-deep traps in DLTS measurements. The dependence of EM2 peak height on the duration of filling pulse and the detailed analysis of CTS showed that the trap EM2 spectrum consisted of three electron traps which had thermal emission activation energies of approximately 0.35 eV and various capture cross sections with activation energies for electron capture. On the other hand, the trap EL6 spectrum in n-type LEC GaAs was described by two levels of traps with activation energies of 0.32 eV and 0.33 eV for electron emission, respectively. It was concluded that so-called EL6 formed a family and some of its components were classified as defects with large lattice relaxation.
INTRODUCTION It is important to understand properties of deep levels in semiconductor materials for device application and physics. In the case of GaAs, a great deal of effort has been devoted to studies of the mid-gap donor EL2 that plays a dominant role in semi-insulating materials. In contrast to this, the medium-deep traps in GaAs have drawn much less attention [1,2,3,4], presumably because the concentrations of medium-deep traps are one order of magnitude less than that of EL2. However, medium-deep traps are also expected to influence electrical characteristics of pure GaAs crystals, where concentrations of those traps are comparable to those of impurities. In the present investigation, the properties of medium-deep electron traps in n-type PCZ and LEC GaAs bulk materials were studied by using capacitance transient spectroscopy (CTS) and temperature dependent Hall (TDH) measurements. The PCZ method, in which a GaAs crystal is grown under arsenic pressure without any encapsulant in a hot wall chamber[5], has a potential to control crystal stoichiometry and to decrease defect density.
Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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EXPERIMENTAL Free carrier concentrations at 300 K in n-type PCZ and LEC samples used in this study were 8 x 101 cm-' and 8x 10s5 cm-3 , respectively. Siand S were found to be dominant shallow donor impurities in the PCZ samples from secondary ion mass spectroscopy. The origin of these impurities was hot wall chamber materials and the concentrations could be reduced by improvements of chamber materials to a level where undoped semi-insulatin
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