Limitations in Time Resolved Photoluminescence of Gallium Nitride Using a Streak Camera

Semiconductor performance is often characterized in terms of the rate at which its carrier recombination processes occur. Carrier recombination, including radiative, and Schockley-Read-Hall and Auger (both nonradiative), occurs at ultra-fast times in the picosecond or femtosecond regimes. A device which can measure both spectral data and temporal phenomena at this speed is the streak camera. The capability to do time-resolved spectroscopy of wide band gap semiconductors using a streak camera has been established at AFIT for the first time. Time resolved photoluminescence (TRPL) from samples of gallium nitride were measured at temperatures of 5 K over spectral bands of 36.6 A and temporal ranged of 45 to 1970 ps, both instrument-limited. TRPL features at 3552 A and 3587 A were studied giving decay lifetimes at 43.2 plus or minus 1.6 ps and 16.8 plus or minus 3.4 ps, respectively. Shockley-Read-Hall, Radiative and Auger coefficients were found but parameterized in terms of experimental efficiency, n, which was not measured. These values, determined using a least-squares-error fit of the carrier recombination rate equation to collected data, are -9.3*10 9 plus or minus 4.9*10 8 s -1, 7.5*10 17 n plus or minu 8.0*10 19 n cm 3/s, and 1.8*10 25 n 2 plus or minus 8.6*10 27 n 2 cm 6/s respectively, for the first peak and -2.5*10 10 plus or minus 5.2*10 9 s -1, 4.9*10 19 n plus or minus 2.0*10 19 n cm 3/s and -1.4*10 28 n 2 plus or minus 8.6*10 27 n 2 cm 6/s for the second peak. Since alignment of the streak camera has not yet been optimized, large but unquantified uncertainty in these results exists. Isolating vibratiosn and improving streak camera alignment should reduce the uncertainty and permit data collection temporally resolved at hundreds of femtoseconds.