A SCHEMATIC STUDY OF EL-2 (0-) LEVEL IN GALLIUM ARSENIDE

Abstract

A study of band structure of GaAs and related III-V ternary and quarternary compounds has been carried out. Properties of deep levels in semiconductors are presented. Various techniques to characterise deep levels in semiconductors are also discussed. Growth technques for III-V semiconductors have also been studied. Finally a schematic study of origin of EL-2 level in GaAs has been presented. A reanalysis of time dependence of capacitance to characterise trap levels with long time constants has also been presented. Following conclusion have been drawn regarding the 0.83 eV, electron trap level (EL-2) in GaAs : (1) It is not due to Ga vacancy, (2) It is not due to oxygen to which it has been associated for a very long . time and ultimately named as oxygen level. (3) It is not a complex involving oxygen. On this controversy, a reanalysis of results show that the level is probably formed due to excess of As atoms on Arsenic sites. Many experimental results tend to suggest this proposition. Further 0.76 eV electron trap level is a level different than EL-2 at 0.83 eV. This confusion has been existing in the literature till now. This 0.76 eV level is probably due to oxygen. Properties of 0.64, .eV hole trap level law also been presented. A better analysis of Capacitance - time measurements on p-n junction/schottay barrier diodes has been presented which offers the advatange of chacterising the deep level with long time costants without recording the full transient at all temperatures ro.1uirod . This method proposes to save a lot of time and expenditure regarding such characterization. The 0.83eV EL-2 and 0.76eV levels detected in many samp-les have so far been taken to represent the same level. The apparent discrepancy in the energies has been assigned to the experimental errors involved. It has been shown in the present work that these two are two different levels and the 0.76eV level is possibly due to oxygen, while 0.83eV (EL-2) level is associated with As rich conditions in the crystals.