What question did this study set out to answer?

The aim is to investigate how dielectric encapsulation affects the Al-Ga interdiffusion in quantum-well heterostructures.

February 15, 1987

Effects of dielectric encapsulation and As overpressure on Al-Ga interdiffusion in AlxGa1−x As-GaAs quantum-well heterostructures

Key Points

The aim is to investigate how dielectric encapsulation affects the Al-Ga interdiffusion in quantum-well heterostructures.
Measured Al-Ga interdiffusion coefficient (DAl-Ga) under various encapsulation conditions.
Analyzed activation energy for interdiffusion with different encapsulants, including SiO2 and Si3N4.
Studied strain effects on encapsulation geometry (e.g., stripes) affecting interdiffusion anisotropy.
DAl-Ga for dielectric-encapsulated samples is significantly lower than for capless and SiO2-capped samples.
Activation energy for interdiffusion in dielectric samples is approximately 3.5 eV, compared to 4.7 eV without encapsulation.
Interdiffusion coefficient for Si3N4-capped samples is nearly an order of magnitude smaller than for capless or SiO2-capped samples between 800°C and 875°C.

Abstract

Data are presented showing that the Al-Ga interdiffusion coefficient (DAl-Ga) for an AlxGa1−xAs-GaAs quantum-well heterostructure, or a superlattice, is highly dependent upon the crystal encapsulation conditions. The activation energy for Al-Ga interdiffusion, and thus layer disordering, is smaller for dielectric-encapsulated samples (∼3.5 eV) than for the case of capless annealing (∼4.7 eV). The interdiffusion coefficient for Si3N4-capped samples is almost an order of magnitude smaller than for the case of either capless or SiO2-capped samples (800≤T≤875 °C). Besides the major influence of the type of encapsulant, the encapsulation geometry (stripes or capped stripes) is shown, because of strain effects, to be a major source of anisotropic Al-Ga interdiffusion.

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