PROPERTIES OF THE DEEP DONOR STATES OF ALXGA1-XASSE

A study of the electrical and optical proper-ties of the Se deep donor states in AlxGa1-xAs:Se grown by metalorganic vapor phase epitaxy (MOVPE) process is reported. A novel experimental technique is presented to determine the absolute energy and the true density of the deep donor. The characteristics of the Se deep donor states are obtained from deep level transient spectroscopy, photoluminescence, photocapacitance, Hall effect measurements, isothermal capacitance transient measurements, and a quasistatic capacitance voltage technique. It is found that the Se dopant gives rise to at least two energy levels in the band gap. One is the generally observed deep donor level, commonly called the DX level and the other is a new shallower donor state which also exhibits DX-like properties. The concentration of the shallower state is less than 5% of the deep donor density. The densities of both donors increase with the mole fraction of H2Se used during MOVPE growth. Thermal emission activation energies of 0.29 +/- 0.01 and 0.24 +/- 0.01 eV were found for the deep and shallower donor states, respectively, for 0.23<x<0.41. The Se donor ionization energies relative to the GAMMA minimum are determined for samples with different AlAs mole fractions, and also, the true densities of Se donors are obtained. We propose a macroscopic model for the emission and capture mechanisms of Se donors in AlxGa1-xAs, which allows a consistent interpretation of the results obtained by different measurement techniques and provides a natural explanation for the low temperature Hall density saturation phenomenon and the persistent photoconductivity effect.