Investigation of N2 plasma GaAs surface passivation efficiency against air exposure: towards an enhanced diode
Résumé
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 °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 (×4), 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 °C), yielding a 3.1 nm-thick GaN layer. However, for nitridation temperatures above 300 °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.
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