Investigation of N-2 plasma GaAs surface passivation efficiency against air exposure: Towards an enhanced diode

GaAs(001) substrates nitrided with N-2 plasma at various temperatures were investigated after being exposed to air for 40 days. They were studied by means of parallel angle-resolved X-ray photoelectron spectroscopy, scanning electron microscopy, micro-photoluminescence and time-resolved photoluminescence (TRPL). Several nitrided GaAs Schottky diodes were manufactured to find the optimal nitridation conditions for high diode quality. An improvement on the ideality factor was achieved for a diode with 1.3 nm-thick GaN layer grown at room temperature and crystallized at 620 degrees C. The crystallization process was needed to enhance the air-exposed GaAs photoluminescence efficiency by a factor 15. TRPL measurements showed a spectacular increase in the decay time (x4), even for a sample exposed to air for 2 years. A high level of GaAs surface chemical protection was achieved. Indeed, neither the element arsenic As-0 nor Ga and As oxides states were detected at the GaN/GaAs interface for nitridation at high temperature (500 degrees C), yielding a 3.1 nm-thick GaN layer. However, for nitridation temperatures above 300 degrees C, pits with an inversed pyramidal shape and square base were formed at the surface, their size increased as nitridation temperature was raised. These pits acted as non-recombination centers which reduced the GaAs photoluminescence yield.