Electroluminescence at GaN and Ga[sub x]In[sub 1−x]N Electrodes in Aqueous Electrolytes

Abstract

Electroluminescence (EL) of single crystal and thin films of GaN and Ga x In 1-x N (x = 0.8) was observed in aqueous solution containing peroxydisulfate on passage of cathodic currents. The resulting emission was compared with the photoluminescence of the same materials on ultraviolet light excitation. Only the subbandgap emission was observed in EL for GaN electrodes. The position and intensity of this emission peak depended on the applied potential, with a significant blue shift observed with increasing applied potential. The EL spectra of Ga x In 1-x N only showed a yellow luminescence band at lower applied potentials. When a more negative potential was applied, the near-bandedge emission (2.9 eV) appeared. © 1998 The Electrochemical Society. S1099-0062(98)03-062-4. All rights reserved.Manuscript submitted March 14, 1998; revised manuscript received June 17, 1998. Available electronically July 9, 1998.The III-V nitride semiconductors and their ternary compounds have recently attracted significant interest because of their potential use in optoelectronic devices, such as visible and ultraviolet (UV) light emitting diodes (LEDs) and lasers. It was mainly the realization of bright blue and green LEDs based on GaN heterostructures that spurred the increased efforts in making and understanding the properties of these materials. 1 InN, GaN, and AlN are direct bandgap semiconductors with bandgap energies of 1.9, 3.4, and 6.2 eV, respectively. The size of the bandgap can be manipulated, with energies ranging from the red region in the visible to the deep UV region, by varying the composition of the ternary materials. 2 While the optical characterization of these compounds by photoluminescence (PL) and solid-state electroluminescence (EL) has been extensively investigated, no reports of solution phase EL have appeared. Light can be generated at semiconductor electrodes through electron-hole recombination by the use of specific electrode reactions. The principles of this experiment are shown in Fig. 1. In this article, we report the EL properties of single crystal n-type GaN and Ga x In 1-x N thin films and bulk single crystal electrodes in the presence of peroxydisulfate. Experimental The GaN and Ga x In 1-x N (x = 0.8) thin film electrodes in this study were grown by low-pressure metallorganic chemical vapor deposition (MOCVD) on sapphire substrates. 3,4 The primary precursors employed were trimethylgallium (TMGa), trimethylindium (TMIn), ammonia (NH 3 ), and silane (SiH 4 ) for the n-type doping. The Si-doped GaN thin film was 1.5 µm thick and the Ga x In 1-x N thin film was 200 nm thick on a 1.5 µm thick GaN layer. Bulk single crystals of GaN were synthesized by heating NaN 3 and Ga metal in a stainless steel tube sealed under nitrogen atmosphere at 600-800°C for 24-96 h. 5 Larger single crystals, with dimensions > 0.1 mm, were prepared at 700-800°C with 3 mmole of NaN 3 . 5 GaN single crystal electrodes (0.6-0.7 mm) were used for this study. These electrodes were etched in 1 M KOH at 70°C for 25 s before a series ...