ABSTRACT
R e g io n s ....................................................................................... 279 3. InGaAs/InP Superlattice Mixing and Conversion............................. 283 4. Control of Layer Intermixing for Device Applications . . . . 287
4.1. Differential Al-Ga Interdiffusion in AlGaAs and AlGalnP Quantum W e lls ........................................................................... 287
4.2. Selective Intermixing of Single Modulation-Doped GaAs Quantum W e l l ........................................................................... 293
4.3. Selective Intermixing of Dual Modulation-Doped GaAs Quantum W e lls ........................................................................... 299
5. S u m m a ry ....................................................................................... 304
III-V semiconductor superlattices have an excellent thermal stability against the inter-diffusion of constituents across the heterojunction under typical processing conditions. For example, the inter-diffusion coefficient of Al in an AlAs/GaAs superlattice at 850°C is on the order of IO-18 cm2/sec [1]. This stability, however, can be rapidly reduced by introducing impurities or lattice defects. It was first demonstrated by Laidig et al. [2] that introducing Zn into GaAs/AlAs superlattices could dramatically increase the interdiffusion of Al and Ga by a large factor in 1981. Since then, evidence of superlattice mixing induced by a variety of dopants, both n-type and p-type, has been reported. Examples of these species are Si, Ge, C, Te, Se, S, Sn, and Be [3-9]. These
impurities can be introduced either during the growth or post growth from external sources. Besides introducing impurities, superlattice intermixing can be implemented by internal defect migration through an anneal process where a S i02 surface cap is utilized as a diffusion sink for Ga. The migration of the Ga vacancies from the surface into the structure results in an enhancement of A1 and Ga interdiffusion in the superlattice [10]. Alternatively, the mixing of a superlattice can be realized by ion implantation which generates atomic displacement in the superlattice by collision effect.
