Fabrication of Self-Assembling AlGaN Quantum Dot on AlGaN Surfaces Using Anti-Surfactant
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Cite this article as: MRS Internet J. Nitride Semicond. Res. 4S1, G9.4(1999) ABSTRACT We report on the first artificial fabrication of self-assembling AIGaN quantum dots (QDs) on AIGaN surfaces using metal organic chemical vapor deposition (MOCVD). The AIGaN QDs are fabricated using a growth mode change from 2-dimensional step-flow growth to 3-dimensional island formation by modifying the AIGaN surface energy with Si anti-surfactant. The average lateral size and the thickness of fabricated AlGaN QDs, as determined by AFM, are approximately 20 nm and 6nm, respectively. The dot density was found to be controlled from 5x10' 0 cm-2 down to 2x109 cm-2 by increasing the dose of Si anti-surfactant. We obtained the photoluminescence (PL) from AIGaN QDs embedded with AI0. 38Ga 0 .62N capping layers. The Al incorporation in AIGaN QDs was controllable within the range of 1-5 %.
INTRODUCTION GaN and related nitrides are currently of great interest for the application to optical devices in the visible and ultraviolet (UV) energy range. The progress of blue laser diodes (LDs) or blue-green light-emitting diodes (LEDs) are extremely remarkable in recent years [1-3]. High-power and longlifetime InGaN multi-quantum well lasers was already achieved[ I]. AIGaN alloy is useful material for UV optical devices, because of wide bandgap direct transition emission between 3.4eV (GaN) and 6.2eV (AIN). The wide transition range of AlGaN covers the lasing wavelength range achieved by UV gas or solid state lasers, for example, XeCI(308nm) or KrF(248nm) excimer lasers, N2(337nm), He-Cd(325nm) or SHG-Ar(257nm) lasers. UV semiconductor lasers are very attractive in comparison with gas or solid state lasers because of small size. long lifetime, high efficiency, low driving power and CW lasing operation. CW-UV lasers using A1GaN material in the near future will take the place of UV gas or solid state lasers. For the realization of the UV semiconductor lasers, we should clear several technical barriers such as current injection through high Al content AIGaN crystals or efficient UV emission from AIGaN alloy. Especially, the realization of high optical gain in UV emission range of AIGaN alloy is most important for using it as active region of UV lasers. However, it is theoretically predicted that the reduction of the transparency carrier density is difficult in III-nitride material lasers because of a large effective mass [4] in comparison with GaAs or InP based materials. In order to realize the high optical gain necessary in UV semiconductor lasers, the use of low dimensional quantum structures is quite useful. Optical gain enhancement using a exciton-related emission is theoretically predicted and expected even at room temperature, due to the large binding energy of exciton in GaN-related quantum dot structures [5]. It has been reported that the quantum efficiency of InGaN-based quantum well lasers is enhanced by the effect of localized excitons in nano-scale In segregated (In-rich) regions of the quantum well [6]. It is desirable to obtain a str
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