STREEM Software for Strain Engineering in AlGaN-Based Structures
STREEM AlGaN is a specialized software tool for self-consistent modeling of the evolution of epitaxial stress, bow, and dislocation dynamics during the growth and cooling of (0001) III-Nitride heterostructures by MOCVD on silicon, sapphire, SiC, GaN and AlN wafers. It includes simulation of the following phenomena:
- Evolution of heterostructure curvature at the heating, growth, and cooling stages of the growth process;
- Effect of process parameters on stress evolution and dislocation dynamics;
- Crack formation during the growth and cooling of the structure;
- Influence of the recipe on the through-wafer temperature drop and its contribution to the structure bow;
- Processing of in-situ curvature data to retrieve stress state in the particular layers
To predict relaxation of compressively stressed (Al)GaN layers, a model has been developed, attributing relaxation to nucleation and inclination of threading dislocations depending on the process conditions and stress state. As a result of the modeling, the user can analyze the stress, curvature, bow, effective lattice parameter, density and inclination angle of threading dislocations in the epitaxial stack. By adjusting the recipe, including the temperature, thickness and composition of the layers, sequence and durations of the particular stages of the process, one can follow the respective changes in the above characteristics and establish correlations between the recipe and properties of the heterostructure.
Example 1: Structure with graded AlGaN buffer
This example is based on experiment by B. Krishnan et al., Sensors and Materials 25 3 (2013) 205. We simulate curvature evolution in the epitaxial structure with graded AlxGa1-xN buffer grown on 8″ Si substrate in a vertical high-speed rotating-disk MOCVD system, see the schematic view on the right. It is demonstrated that the software is capable of reasonably reproducing the curvature evolution including the growth of graded AlGaN buffer, thick GaN layer, and the cooling stage, see below. The growth procedure starts with the AlN nucleation layer (NL) whose stress state is not modeled directly, but the respective mismatch relaxation degree can be found via processing of in-situ curvature data. In this case, the threading dislocation density at the first AlGaN/AlN interface remains the only parameter required to fit by the user. Combined with the mismatch relaxation degree in the NL it can serve as the basis for all the subsequent predictive strain engineering based on the same growth recipe for the nucleation layer.
Schematic view of the stack, B. Krishnan et al., Sensors and Materials 25 3 (2013) 205
Comparison of calculated and experimental curvature evolution: (1): AlN nucleation layer; (2): AlGaN graded buffer; (3): thick GaN layer; (4): AlN interlayers; (5): cooling
Detailed view of stress and threading dislocation density evolution during growth of the graded AlGaN buffer
Example 2: Modeling of GaN/AlN Superlattice Buffer Structure
Experiment: E. Feltin et al., Appl. Phys. Lett. 79 (2001) 3230
This case represents one of the first examples for successful application of superlattices as dislocation filters in developing in GaN-on-Si buffer structures.
Application of AlN/GaN superlattices (SL) is another possible approach to efficiently reduce the threading dislocation density and counteract the tensile stress usually observed in the growth of GaN on Si wafers. The compressive stress induced by AlN layers in subsequent GaN layers of SL results in significant inclination of existing dislocations and their annihilation, while the GaN layers do not exceed critical thickness necessary for nucleation of new dislocations. Combined, these effects result in significant reduction of the dislocation density. In this example, we illustrate that STREEM AlGaN can be successfully used to model TDD and stress evolution during growth and cooling of such GaN-on-Si structure with different number of AlN/GaN SLs and thickness of the top GaN layer.
Reduction of TDD in the heterostructure with four GaN/AlN SLs separated by 200 nm GaN
Dependence of TDD on the number of superlattices: comparison with experimental data
Experimental and calculated in-plane strain of the top GaN layer in dependence on the number of AlN/GaN SLs
“Analysis of strain and dislocation evolution during MOCVD growth of an AlGaN/GaN power high-electron-mobility transistor structure” by Mikhail Rudinsky, Eugene Yakovlev, Roman Talalaev, Tomas Novak, Petr Kostelnik, and Jan Sik, joint work with ON Semi, Japanese Journal of Applied Physics 58, SCCD26 (2019)
“Analysis of strain and dislocation evolution during MOCV Dgrowth of AlGaN/GaN power HEMT structure” by Roman Talalaev, Mikhail Rudinsky, Eugene Yakovlev, Tomas Novak, Petr Kostelnik and Jan Sik, IWN 2018 (2018)
“Modeling of bowing, stress and threading dislocation density evolution in III-nitride heterostructures grown on Si substrate” by Yuji Mukaiyama, Mikhail Rudinsky, Roman Talalaev, Momoko Deura, Takuya Nakahara, Takeshi Momose, Yoshiaki Nakano, Masakazu Sugiyama and Yukihiro Shimogaki, IWMCG-9 (2018)
“Stress‐dislocation management in MOVPE of GaN on SiC wafers” by M. E. Rudinsky, E. V. Yakovlev, W. V. Lundin, A. V. Sakharov, E. E. Zavarin, A. F. Tsatsulnikov, L. E. Velikovskiy, PSS (A) Applications and Materials 213(10), DOI: 10.1002/pssa.201600210 (2016)
“Strain engineering for electronic devices: modeling capabilities” by S.Yu. Karpov, M.E. Rudinsky, A.V. Lobanova, E.V. Yakovlev, and R.A. Talalaev, ICCGE-18 (2016)
“Control of Stress, Bow, and Dislocation Density in (0001) AlN/GaN Superlattices Grown on Silicon” by M.E. Rudinsky, A.V. Lobanova, E.V. Yakovlev, and R.A. Talalaev, IWN 2016 (2016)
“Stress-dislocation management in MOCVD of GaN on SiC wafers” by W.V. Lundin, A.V. Sakharov, E.E. Zavarin, A.F. Tsatsulnikov, M.E. Rudinsky and E.V. Yakovlev, ISGN-6 (2015)
“Контроль напряжений и плотности дислокаций в технологии GaN-on-Si”, М.Э. Рудинский, А.В. Лобанова, Е.В. Яковлев, М.С. Рамм, Р.А. Талалаев, 10-я Всероссийская конференция НИТРИДЫ ГАЛЛИЯ, ИНДИЯ И АЛЮМИНИЯ – СТРУКТУРЫ И ПРИБОРЫ (2015)
More on Model Development
“Model of tensile stress relaxation in thin (0001) Al(Ga)N layers” by Mikhail Rudinsky, Sergey Karpov, Roman Talalaev, Wsevolod Lundin, DRIPXVIII (2019)
“Impact of metalorganic vapor phase epitaxy growth conditions on compressive strain relaxation in polar III-nitride heterostructures” by Mikhail E. Rudinsky, Anna V. Lobanova, Sergey Yu. Karpov and Roman A. Talalaev, JJAP 58(SC):SC1017 (2019), DOI: 10.7567/1347-4065/ab06b7