Photoluminescence of FS-GaN Treated in Alcoholic Sulfide Solutions
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Cite this article as: MRS Internet J. Nitride Semicond. Res. 4S1, G6.14(1999) Abstract
Results are presented on the photoluminescence of n-GaN (T=300 K) after surface treatment with sulfide (Na 2S and (NH 4 )2S) solutions in water or isopropyl alcohol. It has been shown that the intensity of the n-GaN photoluminescence band is enhanced as a result of the surface treatment with alcoholic sulfide solutions, this enhancement being greater for a strongly basic Na2 S solution than for a weakly basic (NH4)2S solution. Introduction The progress in UV semiconductor optoelectronics relies not only on the advance of fabrication methods of III-V nitrides but on the surface treatment methods as well. In the last years a number of studies [1-3] was published dealing with modification of the electronic properties of the GaN surface treated with liquid or gaseous agents. For chemical treatment in solutions, both acids and bases are used: HC1, HF, NH 4F, HNO 3, H2SO 4 , H 3PO 4, H20 2, NH 4OH, NaOH, KOH [3]. Studies of the electronic properties of Ill-V semiconductor surfaces aim first of all at reducing the surface recombination velocity, increasing the photoluminescence quantum yield and so on. To achieve modification of the surface electronic properties, aqueous [4] or alcoholic [51 solutions of sulfides (Na 2S and (NH 4) 2S) can be used. In this study an attempt was undertaken to apply the technology of surface passivation employing alcoholic sulfide solutions in order to improve the electronic properties of GaN, in particular, the photoluminescence intensity. Experiment The specimens under study were n-GaN layers (n=5x 108 cm3 ) of a thickness 200-400 ýtm grown on sapphire substrates by chloride gas transport epitaxy [6]. After termination of the epitaxial growth process the layers were separated from the substrate (free-standing GaN). Chemical treatment of the GaN surface was performed by dipping the semiconductor specimen at room temperature for 1 min into one of the following solutions: 10% aqueous
G 6.14 Mat. Res. Soc. Proc. Vol. 537 © 1999 Materials Research Society
solution of (NH4 )2S, 1% solution of (NH4) 2S in isopropyl alcohol (i-C 3H7 OH), and saturated Na 2S solutions in water or isopropyl alcohol. The room temperature photoluminescence was excited with a pulsed nitrogen laser (X=337 nn, I=20 W). The experimental setup was similar to that of Ref. [7]. Results The experimental results are as follows. The photoluminescence intensity of nGaN increased as a result of the sulfide treatment of the surface in solutions of both sodium sulfide and ammonium sulfide (Fig.1). The most pronounced intensity increase (by a factor of 3.6) compared with the intensity of untreated n-GaN was observed for treatment with the saturated solution of Na2S in isopropyl alcohol.
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hv, eV Fig. 1. Photoluminescence spectra of the n-GaN surface after sulfidizing in one of the following four solutions: 10% aqueous solution of (NH4) 2S (2), 1% solution of (NH 4)2S in isopropyl alcohol (i-C
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