Data on thermally stimulated current (TSC), Hall mobility, photocurrent, and photovoltage measurements associated with EL2 transition to the metastable state in semi‐insulating (si) GaAs are presented. The metastable behavior of EL2 enables the separate observation of electron and hole traps by thermally stimulated methods. Thermal quenching of TSC, associated with the hole trap H2 = Ev + 0.4 eV, is observed for the first time. The influence of inhomogeneous distribution of defects is discussed.
Thermal quenching of thermally stimulated conductivity has been considered theoretically assuming a model with three types of states in the bandgap of a semiconductor. It has been shown that the contribution of minority charge carriers to thermally stimulated conductivity might distort the shape of a peak or even change the number of peaks observed. Our model involves traps for majority and minority charge carriers as well as recombination centres. A set of equations is solved in a quasi-stationary approximation. For weak re-trapping of electrons and holes, an analytical solution has been obtained. Other cases have been analysed numerically. Since the minority charge carrier density may be of the same order of magnitude as the majority charge carrier density, which is observed experimentally as the inversion of polarity in the Hall effect or thermo-electromotive force, the bipolar conductivity should also be revealed in the thermally stimulated conductivity phenomenon, and this paper confirms it. The experimental thermally stimulated conductivity curves observed in single crystals of GaAs have been interpreted using the proposed model. The estimation of trap parameters taking into account the contribution of minority charge carriers has been discussed.
The paper presents a theoretical consideration and computation of thermally stimulated conductivity (TSC), assuming fluctuations of potential in a semi-insulating material. The obtained results are compared to TSC data in a homogeneous semiconductor. The computation technique is suitable for general case as well as for weak and fast re-trapping of charge carriers. It has been demonstrated that the maximum of the TSC broadens when fluctuations of potential are taken into account. The possibility of estimating the energy of traps from computed TSC curves is discussed.
Different methods of trap parameter measurement are analysed. Transient
photoconductivity and thermally stimulated effects were used to investigate the
influence of traps in LEC SI-GaAs and high resistivity epitaxial GaAs. The
peculiarities of the TSC were analysed and shown to be related to the influence
of crystal micro-inhomogeneities.Comment: Invited talk, 6-th Workshop on Gallium Arsenide and Related Compounds
June 22-26, 1998 Praha-Pruhonice, Czech Republi
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