ABSTRACT
GaAs and Alo.33Gao.67As layers are grown on (001) semi-insulating GaAs substrates by MBE at 590°C using Ga, A1 and As solid sources. Atomic N is produced using N2 molecules cracked by a tungsten filament.9) In this experiment the N sheet concentration is fixed approximately at 1 X 109cm ' 2 because the N-ALD GaAs layer with this N sheet concentration shows a series of sharp and strong PL lines. The concentration of N atom was estimated by using secondary ion mass spectrometry (SIMS) at high concentrations. However, for lower N atom concentrations below the detection limit of SIMS (5 X 1016cm'3), the concentration was estimated from the efficiency by the hot W filament.9) The N-ALD layer is inserted either at the center or at the position shifted toward the surface heterojunction of Alo.33Gao.67As /GaAs. The structure of a N-ALD Alo.33Gao.67As/GaAs SQW with a 20nm well width is shown in Fig. 1. Semi-transparent Cr-Au film and thick Au-Ge-Ni film are evaporated on the surface and the back surface respectively in order to apply an electric field in the vertical direction. The PL measurements are performed at 10K using an Ar+ ion laser operating at 488nm. High-resolution measurements are performed using lock-in system at very low excitation intensity (1.5mW/cm2).
