STREEM InGaN

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Figure 1. V-shaped edge-type dislocation half-loop

STREEM-InGaN is a specialized software tool for modeling the characteristics of (0001) III-Nitride device heterostructures grown by MOCVD from conventional metal-organic precursors (TMIn, TMGa/TEGa, TMAl) and ammonia, diluted in H2/N2 carrier gases. STREEM-InGaN focuses on an InGaN-based active region which implies a sequence of quantum wells and barriers as well as other stages in-between. Layers grown prior to and after the active region can be added into the simulations as well.

The software is aimed at understanding and control of the structure properties by adjusting the process recipe. In particular, the following issues can be addressed:

– influence of the process parameters on indium incorporation into the quantum wells;

– predictions of the actual composition profile in the active region of the heterostructure, including delayed indium incorporation into the QWs and indium tails in the cap layers or barriers. Due to indium surface segregation, the actual composition profile normally deviates from the nominal one built up from the steady-state solutions obtained for every individual epilayer at the respective growth conditions;

– consistent computations of indium incorporation and elastic energy allows the users to follow and adjust the strain distribution in the active region by both modifying the operating parameters for the

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Figure 2. Increase in the indium content due to partial stress relaxation

particular layers and adding strain-relief layers underneath the active region. The actual composition and strain profiles determine the distribution of the polarization charges in the structure that can be accounted for in subsequent modeling of device operation with the SiLENSe software [http://www.str-soft.com/products/SiLENSe/];

– the onset of stress relaxation via formation of V-shaped dislocation half-loops and subsequent evolution of the strain, threading dislocation density, and indium composition profile can be studied with the STREEM-InGaN software, depending on the particular parameters in the recipe.

As a result of the modeling, the user can analyze such characteristics as the growth rate and composition profile across the heterostructure and the distributions of strain and dislocation density. By adjusting the recipe parameters, including temperature, pressure, flow rates of the precursors and carrier gases, as well as the sequence and durations of the particular stages of the process, the user can follow the respective changes in the above characteristics and establish correlations between the recipe and properties of the heterostructure.

 

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Figure 3. Visualization of growth rate, composition, effective lattice constant, dislocation density, and strain tensor components vs time and thickness

 

 

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