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We conducted a modeling study of the threading dislocation behavior in chirped and unchirped InGaAs/GaAs (001) strained-layer superlattices (SLSs) using a Dodson & Tsao / Kujofsa & Ayers (DTKA) type plastic flow model. Four types of SLSs were investigated: type I was chirped using compositional modulation, type II was chirped using layer thickness modulation, type III was unchirped with alternating layers of InGaAs and GaAs, and type IV was unchirped with alternating layers of InGaAs having two different compositions. Generally the surface and average values of the dislocation density decreased with increasing total thickness. The dependence on top indium composition was more complex, due to dislocation compensation and multiplication effects, but for type II and IV superlattices, the average and surface threading dislocation densities increased in nearly monotonic fashion with top indium composition. Based on these results, the compositionally-modulated chirped (type I) and InGaAs/GaAs unchirped (type III) superlattices appear to be best suited as buffer layers for metamorphic devices, while the chirped superlattices with layer thickness modulation (type II) and InGaAs/InGaAs unchirped (type IV) superlattices appear to be poorly suited for use as buffer layers for devices containing high indium content.

Metamorphic semiconductor devices often utilize compositionally-graded buffer layers for the accommodation of the lattice mismatch with controlled threading dislocation density and residual strain. Linear or step-graded buffers have been used extensively in these applications, but there are indications that sublinear, superlinear, S-graded, or overshoot graded structures could offer advantages in the control of defect densities. In this work we compare linear, step-graded, and nonlinear grading approaches in terms of the resulting strain and dislocations density profiles using a state-of-the-art model for strain relaxation and dislocation dynamics. We find that sublinear grading results in lower surface dislocation densities than either linear or superlinear grading approaches.

Strained-layer superlattices (SLSs) have been used to modify the threading dislocation behavior in metamorphic semiconductor device structures; in some cases they have even been used to block the propagation of threading dislocations and are referred to in these applications as “dislocation filters.” However, such applications of SLSs have been impeded by the lack of detailed physical models. Here we present a “zagging and weaving” model for dislocation interactions in multilayers and strained-layer superlattices, and we demonstrate the use of this model to the threading dislocation dynamics in InGaAs/GaAs (001) structures containing SLSs.

Since the invention of dislocation sidewall gettering (DSG) in 2000 the technique has been applied extensively in infrared focal-plane arrays and flat-panel displays. However, development of DSG technology has been guided mostly by empirical trials due to the lack of detailed physical models. Here we demonstrate the application of a dislocation dynamics model to evaluate DSG approaches in both ZnS_ySe_1-y/GaAs (001) and InGa_xAs_1-x/GaAs (001) heterostructures. We find that the effectiveness of DSG is strongly dependent on composition in both material systems.

In this paper we describe state-of-the-art approaches to the modeling of strain relaxation and dislocation dynamics in InGaAs/GaAs (001) heterostructures. Current approaches are all based on the extension of the original Dodson and Tsao plastic flow model to include compositional grading and multilayers, dislocation interactions, and differential thermal expansion. Important recent breakthroughs have greatly enhanced the utility of these modeling approaches in four respects: i) pinning interactions are included in graded and multilayered structures, providing a better description of the limiting strain relaxation as well as the dislocation sidewall gettering; ii) a refined model for dislocation-dislocation interactions including zagging enables a more accurate physical description of compositionally-graded layers and step-graded layers; iii) inclusion of back-and-forth weaving of dislocations provides a better description of dislocation dynamics in structures containing strain reversals, such as strained-layer superlattices or overshoot graded layers; and iv) the compositional dependence of the model kinetic parameters has been elucidated for the InGaAs material system, allowing more accurate modeling of heterostructures with wide variations in composition. We will describe these four key advances and illustrate their applications to heterostructures of practical interest.

Chirped superlattices are of interest as buffer layers in metamorphic semiconductor device structures, because they can combine the mismatch accommodating properties of compositionally-graded layers with the dislocation filtering properties of superlattices. Important practical aspects of the chirped superlattice as a buffer layer are the surface strain and surface in-plane lattice constant. In this work two basic types of InGaAs/GaAs chirped superlattice buffers have been studied. In design I (composition modulated), the average composition is varied by modulating the composition of one of the two layers in the superlattice period, but the individual layer thicknesses were fixed. In design II (thickness modulated), the individual layer thicknesses were modulated, but the compositions were fixed. In this paper the surface strain and surface in-plane lattice constant for these chirped superlattices are presented as functions of the top composition and period for each of these basic designs.