The structure and properties of metal-semiconductor interfaces

Data are presented showing that Zn diffusion into an AlAs‐GaAs superlattice (41 Lz∼45‐A GaAs layers, 40 LB∼150‐A AlAs layers), or into AlxGa1−xAs‐GaAs quantum‐well heterostructures, increases the Al‐Ga interdiffusion at the heterointerfaces and creates, even at low temperature (<600 °C), uniform compositionally disordered AlxGa1−xAs. For the case of the superlattice, the diffusion‐induced disordering causes a change from direct‐gap AlAs‐GaAs (Eg∼1.61 eV) to indirect‐gap AlxGa1−xAs (x∼0.77, EgX∼2.08 eV).

Disorder of an AlAs‐GaAs superlattice by impurity diffusion

The process of impurity‐induced layer disordering (IILD) or layer intermixing, in AlxGa1−xAs‐GaAs quantum well heterostructures (QWHs) and superlattices (SLs), and in related III‐V quantum well heterostructures, has developed extensively and is reviewed. A large variety of experimental data on IILD are discussed and provide newer information and further perspective on crystal self‐diffusion, impurity diffusion, and also the important defect mechanisms that control diffusion in AlxGa1−xAs‐GaAs, and in related III‐V semiconductors. Based on the behavior of Column III vacancies and Column III interstitials, models for the crystal self‐diffusion and impurity diffusion that describe IILD are reviewed and discussed. Because impurity‐induced layer disordering has proved to be an important method for III‐V quantum well heterostructure device fabrication, we also review the application of IILD to several different laser diode structures, as well as to passive waveguides. We mention that it may be possible to reali...

Atom diffusion and impurity‐induced layer disordering in quantum well III‐V semiconductor heterostructures

The phenomena of the formation of stacking faults and the enhanced diffusion during the oxidation of silicon are shown to be closely related and to have a common cause. A model is presented which at once can consistently explain various aspects of both phenomena; in particular, it is capable of explaining the crystal‐orientation dependence of these phenomena and the parabolic growth of stacking faults. The model envisages a small incompleteness (∼ 10−3) of oxidation, producing silicon interstitials. A concept is introduced that these excess interstitials, as they supersaturate the lattice, will undergo surface regrowth. The rate of interface regrowth is proportional to the density of surface kinks, which is in turn dependent on the surface orientation. The dependence is described. Quantitative analyses are given for the excess interstitials, the growth of stacking faults, and the enhancement of diffusion. The analyses also show that the stacking‐fault embryos are formed within a very short time of the start of oxidation, usually less than 1 sec, consequently leading to uniform stacking‐fault size. The occasionally observed variation in the size of bulk stacking faults is attributed to a continuous formation of stacking‐fault nuclei (e.g., oxide clusters and precipitates). The absence of a surface regrowth would predict a 1/4 power law of stacking‐fault growth, in contradiction of the experiments.

Formation of stacking faults and enhanced diffusion in the oxidation of silicon

Theoretical calculations are presented for equilibrium concentrations of zinc and oxygen vacancies in ZnO. Results are presented at the sintering temperature, and also at room temperature. Theoretical calculations of reaction constants show that the intrinsic donor is the oxygen vacancy, rather than the zinc interstitial. The depletion of vacancies in the surface region, as the ZnO is cooled from the sintering temperature, is also calculated. Homojunction effects which are caused by such depletion are shown to be small.

D. Shaw

Papers

Atomic diffusion in semiconductors