Optical properties of wurtzite GaN grown by low-pressure metalorganic chemical-vapor deposition

Abstract

We present the results of optical studies on the properties of GaN grown by low-pressure metalorganic chemical-vapor deposition, with emphasis on the issues vital to device applications such as stimulated emission and laser action as well as carrier relaxation dynamics. By optical pumping, stimulated emission and lasing were investigated over a wide temperature range up to 420 K. Using a picosecond streak camera, the free and bound exciton emission decay times were examined. In addition, the effects of temperature and pressure on the optical interband transitions and the transitions associated with impurity/defect states were studied using a variety of spectroscopic methods, including photoluminescence and photoreflectance. The fundamental band gap of GaN was mapped out as a function of temperature using the empirical Varshni relation. The pressure coefficient of the gap was determined using diamond-anvil pressure-cell technique. The hydrostatic deformation potential for the direct Γ band gap was also derived from the experimental results.

Predicted maximum mobility in bulk GaN

“…If we use x-ray values 24 of the elastic tensor, then c L ϭ3.82ϫ10 11 N/m 2 , and our fitted value of E 1 becomes 13.5 eV per unit strain; this compares favorably with a hydrostatic value of 9.2 eV, determined from optical measurements. 21 Also, our fitted value of P Ќ , 0.083, is acceptably close to the theoretical value given above, 0.113. In zinc-blende materials, the piezoelectric scattering strength is often quoted in terms of e 14 …”

Photoreflectance study of exciton energies and linewidths for homoepitaxial and heteroepitaxial GaN layers

“…In the case of heteroepitaxial GaN epilayers, electromodulation spectroscopy ͑including PR͒ was widely used to study energies and broadening of excitonic transitions. [3][4][5][6][7][8][9][10] Because of the residual strain in heteroepitaxial GaN epilayers, it was usually observed that excitonic transitions at 10 K are significantly broadened ͑3-10 meV͒, [3][4][5][6][7][8] whereas the broadening of excitonic transitions for homoepitaxial GaN layers equals 1.5-2 meV according to reflectance measurements. 1 A similar broadening of excitonic transitions should be expected in PR spectra of high quality GaN epilayers grown on bulk GaN substrates.…”

Defect Donor and Acceptor in GaN

“…The bulk Hall mobility m 1 was accurately determined from an iterative solution of the Boltzmann transport equation [22,23]. All of the relevant lattice-scattering parameters were taken from the literature: acoustic deformation potential [24 (normalized to 60 mm), and m 2 56 cm 2 ͞V s. Finally, the equations for n meas (n 1 , m 1 , n 2 , m 2 ) and m meas (n 1 , m 1 , n 2 , m 2 ), given earlier, were fitted to the data of Figs. 1 and 2, respectively, to get fitting parameters N D , N A , and E D .…”