A COMPARATIVE STUDY OF DEEP LEVEL EL-2 EFFECTS IN GALLIUM ARSENIDE

Abstract

GaAs and InP are IIl-V group direct band gap compound semiconductors. These semiconductors are widely used in making integrated circuits, microwave and electro luminescent devices such as LED's, DH lasers, solar cell etc. The electronic properties of these devices are affected by the presence of deep defect levels. These levels act as a trap or recombination centres and their effect is non-negligible. Thus it is necessary to detect and characterize deep levels present in the semiconductors. Since properties of GaAs are affected in the presence of deep levels, knowledge of nature and origin of these levels is of great interest. The EL-2 is a major deep donor level present in a GaAs at 0.82 eV below the conduction band. This is a native point defect and its concentration lies in the order of 1016 em"3. The EL-2 has a technological importance because it compensates the residual acceptor impurities and pins the fermi level at the mid gap position. As a result of this compensation process, semi-insulating GaAs can be manufactured without intentional impurity doping. Many techniques, like LEC, MOCVD, MBE, _etc., are used to grow a single crystal of GaAs. The concentration of EL-2 depends on the stoichiometry of the melt from which the crystal is grown and its given by Nt(EL-2) a (concentration of As/concentration of Ga), where y = 0.5. DLTS is used to extract information about EL-2 defect such as• activation energy, capture cross section, concentration and nature of the defect. The atomic nature and origin of the EL-2 defect is still a matter of controversy. Several models have been suggested for this defect, but none of them accounts for all the properties exhibited by EL-2. As per earlier models, EL-2 is believed to be due to the oxygen impurities or dislocations. But later it was concluded that EL-2 is not related to oxygen at all. We have studied some other proposed models and found that the "arsenic antisite (AsGa) arsenic interstitial" complex is responsible for 0.82eV EL-2 present in GaAs.