Temperature and excitation dependences of active layer photoluminescence in (Al,Ga)As laser heterostructures

Abstract

The excitation and temperature dependences of the active layer photoluminescence intensity in (Al,Ga)As laser heterostructures in the range 75–300 K are described. Of the wafers investigated, in a majority of those grown by molecular beam epitaxy and in all the wafers grown by liquid phase epitaxy, the AlxGa1−xAs (0≤x≤0.08) active layer photoluminescence intensity at any temperature increased linearly with increasing excitation intensity at high power levels (≥100 W/cm2) but decreased very rapidly with decreasing excitation intensity at lower power levels indicative of a p-n junction. Since the excitation intensity required to saturate the losses due to the p-n junction, Psat, increased with increasing temperature, the photoluminescence intensity measured at power levels (typically 1–10 W/cm21) lower than Psat decreased by a factor of 100–1000 on increasing the temperature to 300 K. In contrast, for a few wafers grown by molecular beam epitaxy, the active layer intensity varied linearly with excitation at all power levels and at any temperature suggesting the absence of a p-n junction. Consequently, the intensity for these wafers decreased by only a small factor (<10) as temperature was increased from 75 to 300 K. These wafers were of particular interest since lasers fabricated from them also exhibited reduced temperature dependence of threshold current. Examination of the wafer by secondary ion mass spectroscopy indicated that in the temperature insensitive wafers only the p-type dopant in the active layer, Be, extended for a short distance into the n-type confinement layer creating essentially an isotype structure. A first-order calculation of this structure showed also a reduced temperature dependence of the laser threshold current.