Carrier Trapping and Recombination at Point Defects and Dislocations in MOCVD n-GaN

Abstract

We present the results of an approach that allows the analysis of grown-in defects in n-GaN grown by metal organic vapor phase epitaxy by relating the presence of various structural defects to the concentration and properties of distinct deep levels. Transmission electron microscopy and electron beam induced current (EBIC) microscopy together with post-growth hydrogenation are used to determine the threading dislocation density (TDD) and observe their local electrical activity. In conjunction, deep level optical and transient spectroscopies (DLOS and DLTS, respectively) are used to detect deep levels, determine their concentration and analyze their carrier trapping kinetics for these films. The comparison of EBIC analysis with trap spectra prior and after hydrogenation establishes a strong correlation between two specific levels, at Ec — Et = 0.58 and 1.35 eV, and recombination centers distributed in the field of the GaN films. Further, EBIC analysis shows that, independent of hydrogenation, TDs behave as strong recombination centers, and indicates that there must be a deep level associated with these regions. A level observed at Ec — 2.64/Ev + 0.87 eV is a good candidate to account for the electrical activity of the TDs because it captures both electrons and holes, which is characteristic of recombination centers. This is supported by DLTS analysis of the trapping kinetics for this level that reveals a behavior characteristic of a linear arrangement of point defects likely found along the TDs.