Influence of dislocation on high-electric-field property in semi-insulating GaAs

Abstract

High-electric-field properties such as sub-linear I-V characteristic and low-frequency oscillations (LFOs) have been measured in a low-dislocation-density semi-insulating GaAs crystal. It is found that the sub-linear I-V behaviours and LFO waveforms measured at the cathodes where no dislocations exist are very stable but those measured at the cathodes where several dislocations are observed are not stable but more complicated, which is confirmed from Fourier-transform spectra of LFOs. It is explained that the high-electric-field properties observed here depend on the electrical inhomogeneities induced by the dislocations. IntroductionIt is well known that when the DC electric field over 1 kV/cm is applied to a semi-insulating (SI) GaAs crystal, a sub-linear I-V behaviour is observed and then low-frequency oscillations (LFOs) occur [1]. The LFO phenomena may be understood to occur as a result of field-enhanced capture of electron to EL2 level; that is, the decrease in the free electron concentration due to the field-enhanced capture causes the formation and propagation of a high-electric-field domain. The LFOs cause undesired noises in the actual applications of GaAs FETs [2], and they may be understood as a simple example of nonlinear systems [3]. The sub-linear I-V characteristics, LFO waveforms, and their Fourier-transform spectra (FTS) have been precisely measured by using the three-electrode guard-ring method [4]. It should be noticed that the former experiments [4-6] were made in SI-GaAs crystals with high-dislocation density, because low-dislocation density crystals were not easily available. Therefore, there is no work to investigate the relationship between crystal quality and high-electric-field properties. In the present study, we have investigated the influence of dislocations on these properties with a low-dislocation-density GaAs crystal, which is performed by etching of dislocations in the area of cathode electrode after the I-V, LFO, and FTS measurements. We have found the difference in these properties between at the cathodes where no etch-pit exists and at those where several etch-pits exist are observed. Experimental ProcedureThe experimental setup and the three-electrode guard-ring method employed in the present study are shown in Fig. 1. We can measure precisely, stably, and reproducibly I-V, LFO, and FTS characteristics by using this method, because the electric-field distribution is well controlled and uniform in the sample and the surface leakage current is extremely low and reduced in comparison with the two-electrode method [4].We used a low-dislocation-density (001) GaAs wafer grown by the vertical boat method, whose