R. Enrique Viturro

Optical emission properties of semi-insulating GaAs grown at low temperatures by molecular beam epitaxy

We have used cathodoluminescence (CL) and photoluminescence spectroscopy to observe deep‐level states in GaAs grown at low‐substrate temperatures by molecular beam epitaxy (LT GaAs) and the evolution of these states upon annealing. The as‐grown material shows intense deep‐level emissions which can be associated with an excess concentration of arsenic, mostly present as As‐antisite and As‐interstitial defects. These emissions subside with annealing for a few minutes at temperatures above 450 °C. CL measurements clearly show a dramatically reduced concentration of traps in the post‐growth 600 °C annealed material. Additional measurements carried out on As/GaAs systems indicate a high surface‐recombination velocity for these interfaces. These results account for a diminished role of electronic point defects in controlling the insulative behavior of LT GaAs and strongly supports a ‘‘buried’’ Schottky barrier model, which involves ultrafast recombination of carriers at surfaces of embedded arsenic clusters for...

Low‐energy cathodoluminescence spectroscopy studies of III–V superlattice interdiffusion: Optical emission properties of diffusion associated defects

We report a direct optical observation of process‐specific diffusion‐related deep levels associated with interdiffusion in AlGaAs/GaAs superlattice structures. We have used low‐energy cathodoluminescence spectroscopy (CLS) to investigate the formation and evolution of deep levels for intrinsic, under As overpressure, and Si induced layer intermixing. The spatial distribution of these deep levels strongly correlates with the extent of superlattice intermixing, as measured by secondary ion mass spectroscopy (SIMS) and photoluminescence spectroscopy (PLS). The measured cathodoluminescence emission energies and intensities reveal the important role of impurities in the mechanism of interdiffusion at III–V semiconductor superlattices. In particular, our experimental results strongly suggest that the larger interdiffusion rate of the Si induced layer intermixing process is related to the formation of a deep level associated with an optical emission at 1.3 eV. These results indicate the potential of the low‐ener...

Cathodoluminescence Spectroscopy Studies of Growth Induced Deep Levels at GaInP.

We report a cathodoluminescence spectroscopy study of growth-induced deep levels at GaInP epilayers grown by Molecular Beam Epitaxy under various conditions. This approach allows the identification of deep levels which appear to play an important role in the band to band radiative recombination efficiency of these GaInP films. Control of these electronic defects is crucial for the performance of visible optoelectronic devices.

Identification of Diffusion Associated Defects at III-V Semiconductor Heterostructures

Cathodoluminescence spectroscopy is used to identify diffusion-associated III-V semiconductor defects and establish their role in AlGaAs/GaAs intrinsic and n-type impurity induced interdiffusion (Si, Ge, S, and Se) for various ambient conditions, As- and Ga-rich. These identifications involves the study of the temperature and composition dependence of these deep levels and their correlation with theoretical calculations. Our results reveal Column III vacancies and their complexes as the sole mediators of diffusion.

Mechanisms for N-Type Impurity-Induced Disordering of AlGaAs/GaAs Superlattices

We report on a study of disordering by the in-diffusion of a variety of Group IV and Group VI n-type impurities. Secondary ion mass spectroscopy, electrochemical C-V profiling, photoluminescence spectroscopy, and cathodoluminescence spectroscopy were used to determine the extent of interdiffusion, and the spatial distribution of impurities and native defects for impurity-induced disordering. In all cases, the n-type dopants enhance the Al-Ga interdiffusion coefficient over that due to an As overpressure of 2 atm alone. The Si-induced enhancement has been previously attributed to the change in Fermi level with doping and therefore should account for disordering using other n-type impurities. However, we observe important differences in the interdiffusion characteristics (diffusion rate, dopant profiles, energy and intensity of the deep-level emission) induced by Si or Ge, and that by S or Se. Whereas a strong correlation exists between the carrier concentration profile and the disordered regions in the Si-, Ge-, and Se-doped crystals, little direct correspondence is found for crystals doped with S. Instead, the disordering seems to be determined primarily by the presence of Group III vacancies, as is also the case in undoped crystals disordered by an As ambient alone. In addition, the deep level emission at 1.15 and 1.3 eV, which are associated with vacancy defects, correlates well with the extent of the Al-Ga interdiffusion.

Cathodoluminescence and Photoluminescence Spectroscopy Study of Low Temperature Molecular Beam Epitaxy GaAs

We report a cathodoluminescence (CL) and photoluminescence (PL) study of molecular beam epitaxy grown GaAs at low substrate temperatures (LT GaAs), and semi-insulating LEC GaAs. The as grown LT GaAs material shows intense deep level emissions which can be associated with an excess concentration of Arsenic. These emissions subside with annealing for a few minutes at temperatures above 450 ° C. CL measurements clearly show an extremelly reduced concentration of traps in the post-growth 600 ° C annealed material. These results account for a diminished role of electronic point defects in controlling the insulative behavior of LT GaAs and strongly support the “buried” Schottky barrier model.