Carrier Lifetimes in GaN Revealed by Studying Photoluminescence Decay in Time and Frequency Domains

Abstract

The carrier dynamics in GaN epilayer, grown using migration enhanced metalorganic chemical vapor deposition (MEMOCVD), is investigated in a wide range of photoexcitation power density of twelve orders of magnitude. Study of photoluminescence decay lifetimes at extremely low excitation power densities of 0.5 mW/cm2 was performed using frequency-domain lifetime measurements with a UV LED (280 nm) as an excitation source. The carrier lifetimes at high excitation power densities was studied using time-resolved photoluminescence (TR PL) spectroscopy and light-induced transient grating (LITG) technique. The measurements were carried out in the temperature range from 10 to 300 K. At high carrier densities, which are typical for device applications, the room- temperature carrier lifetime of 2 ns was obtained, while a variety of decay components was revealed at low excitation intensities. Trapping and detrapping of the carriers/excitons is shown to play an important role in the carrier dynamics at low carrier densities.