Thermal Annealing of InGaN/GaN Strained-Layer Quantum Well
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Department of Electrical & Electronic Engineering, University of Hong Kong, Pokfulam, Hong Kong, [email protected] ** Electrical and Computer Engineering and Materials Departments, University of California, Santa Barbara, CA 93106 Cite this article as : MRS Internet J. Nitride Semicond. Res. 4S1, G6.25 (1999)
ABSTRACT Quantum well (QW) material engineering has attracted a considerable amount of interest from many people because of its ability to produce a number of optoelectronic devices. QW composition intermixing is a thermal induced interdiffusion of the constituent atoms through the hetero-interface. The intermixing process is an attractive way to achieve the modification of the QW band structure. It is known that the band structure is a fundamental determinant for such electronic and optical properties of materials as the optical gain, the refractive index and the absorption. During the process, the as-grown square-QW compositional profile is modified to a graded profile, thereby altering the confinement profile and the subband structure in the QW. The blue-shifting of the wavelength in the intermixed QW structure is found in this process. In recent years, III-nitride semiconductors have attracted much attention. This is mainly due to their large bandgap range from 1.89eV (wurtzite InN) to 3.44eV (wurtzite GaN). InGaN/GaN quantum well structures have been used to achieve high lumens blue and green light emitting diodes. Such structures also facilitate the production of full colour LED displays by complementing the colour spectrum of available LEDs. In this paper, the effects of thermal annealing on the strained-layer InGaN/GaN QW will be presented. The effects of intermixing on the confinement potential of InGaN/GaN QWs have been theoretically analysed, with sublattices interdiffusion as the basis. This process is described by Fick’s law, with constant diffusion coefficients in both the well and the barrier layers. The diffusion coefficients depend on the annealing temperature, time and the activation energy of constituent atoms. The optical properties of intermixed InGaN/GaN QW structure of different interdiffusion rates have been theoretically analyzed for applications of novel optical devices. The photoluminescence studies and the intermixed QW modeling have been used to understand the effects of intermixing. INTRODUCTION Wide-bandgap semiconductors such as GaN, AlN, InN and their ternary compounds have been studied so as to realize the semiconductor blue-green laser. As a matter of fact, the demonstration of high-brightness blue-green light-emitting diodes from the wurtzite GaN semiconductor has stimulated a lot of research on the fabrication of blue-green laser diodes using nitride-based semiconductors [1-3]. InGaN/GaN single-quantum-well structures have been used to achieve high-power blue and green light-emitting diodes. Also, room temperature pulsed lasing of a strained InGaN/GaN multiquantum-well laser diode has recently been demonstrated. The nature crystal structure of most of the group III nitrides
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