| We used photoluminescence spectroscopy to study the physics of new and useful semiconductors and semiconductor alloys grown by different techniques or with different alloy composition. We have investigated the optical and structural properties of the GaN epilayers grown by Low-Pressure Chemical Vapor Deposition (LPCVD) using hydrazoic acid (HN3) as a nitrogen source. The growth facility, and the growth procedures are described. We also discuss the advantages of hydrazoic acid as a novel nitrogen source for GaN growth, compared to the widely used ammonia (NH3), such as low growth temperatures of ∼600°C and low V/III precursor ratios of 1 to 10, and high growth rates of several mum/hr. The GaN samples grown by LPCVD on (0001) sapphire substrates were characterized by Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Ultraviolet Photoelectron Spectroscopy (UPS), Raman spectroscopy, X-ray Spectroscopy, Auger Electron Spectroscopy, Far Infrared Transmission spectroscopy, optical absorption, photoluminescence (PL), and time-resolved PL techniques. Extensive characterization of the films shows that they are polycrystalline GaN with significant concentration of impurities an structural defects.;We have carried out a photoluminescence study of the series of GaN samples grown by Metalorganic Chemical Vapor Deposition (MOCVD) on (0001) sapphire with epilayer thickness ranging from 1 mum to 3.3 mum. By analyzing the spectral position of near-bandedge emissions we find that all of the our GaN epilayers are under residual compressive stress with the maximum in-plane compressive strain 3xx=3yy =-1.2x10 -3, resulting in a positive energy shift of the near-bandedge PL emissions. The temperature study of the near-bandedge spectra allowed us to distinguish between bound and free exciton emissions. The lineshape fitting of the 1LO-phonon replica of the (FEA, X) emission with the modified Maxwell distribution function taking into account the inhomogeneous broadening shows that the effective temperature of free exciton subsystem is higher than the lattice temperature (10 K) by ∼15 K. From this we conclude that in our GaN samples free excitons do not reach quasi-thermal equilibrium with the lattice due to the short exciton lifetime. We also observed a distinctive Resonant Raman Scattering effect in bulk GaN at low temperatures with incident photon energy in resonance with free exciton and bound exciton transitions. We observe, for the first time in GaN, a strong Raman resonance with I X bound exciton state.;We have also examined the photoluminescence and photoluminescence kinetics of a series of In1-xGaxP alloys in an effort (1) to elucidate the electronic structure of the conduction band versus alloy composition, especially near the direct-indirect crossover, (2) to determine precisely the composition of the direct-indirect crossover, and its temperature dependence, and (3) to understand the nonradiative decay mechanism, and its temperature dependence. (Abstract shortened by UMI.). |
