Point Defect Management in III-Nitrides: A Systematic Approach

Defect incorporation is dependent on the defect formation energy and hence on associated chemical potentials and the Fermi level. For example, the formation energy of C_N in Al/GaN varies as the chemical potential difference (µ_N- µ_C) and -E_F (Fermi level). Here, we demonstrate a systematic approach to point defect control by employing the defect formation energy as a tool through (a) chemical potential control and (b) Fermi level control. Chemical potential control (µ_N and µ_C) with a case study of C and Si in MOCVD Al/GaN is reported. We derive a relationship between growth parameters, metal supersaturation and chemical potentials of III/N and impurity atoms demonstrating successful quantitative predictions of C incorporation and other corresponding compensating defects as a function of growth conditions in Al/GaN. Hence the growth environment necessary for minimal defect incorporation within any specified constraints may be determined. Fermi level control based point defect reduction is demonstrated by modifying the Fermi level describing the probability of the defect level being occupied/unoccupied i.e. defect quasi Fermi level (DQFL). The DQFL is modified by introducing excess minority carriers (by above bandgap illumination). A predictable (and significant) reduction in compensating point defects (C_N, H, V_N, V_III-nSi) in (Si, Mg) doped Al/GaN measured by electrical measurements, photoluminescence and secondary ion mass spectroscopy (SIMS) provides experimental corroboration. Further, experiments with varying steady state minority carrier densities at constant illumination prove the role of minority carriers and DQFL in defect reduction over other influences of illumination that are kept constant.