MODELING OF STRAIN-INDUCED EFFECTS ON GAN PN JUNCTIONS USING SILVACO ATLAS

ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-11 250 MODELING OF STRAIN-INDUCED EFFECTS ON GAN PN JUNCTIONS USING SILVACO ATLAS A.I.Mamadjanov1., H.Olimxonova1 (student) 1University of Business and Science. 111, Zarbdor str, Namangan, Uzbekistan. ABSTRACT In this work, a comprehensive numerical analysis of the influence of mechanical strain on Gallium Nitride (GaN) PN junctions is presented using Silvaco ATLAS. The study considers both compressive and tensile strain in the range of ±0.5%, analyzing their effects on the built-in potential, electric field distribution, carrier density, and current–voltage (I–V) characteristics. The results demonstrate that strain-induced piezoelectric polarization significantly alters the junction properties by modifying the internal electric field and depletion region width. These findings underline the critical role of strain engineering in optimizing GaN-based optoelectronic and power devices. 1. INTRODUCTION Gallium Nitride (GaN) has emerged as a key wide bandgap semiconductor material due to its superior electrical, thermal, and chemical properties. With a bandgap of approximately 3.4 eV, high breakdown voltage, and excellent thermal conductivity, GaN-based devices are widely employed in power electronics, light-emitting diodes (LEDs), and high-electron-mobility transistors (HEMTs). However, the piezoelectric and spontaneous polarization characteristics of GaN significantly influence the electronic behavior of its junctions. The mechanical strain induced during epitaxial growth or device operation can modify the energy band structure, built-in potential, and carrier transport mechanisms. Although extensive studies have focused on AlGaN/GaN heterostructures, the fundamental strain response of homojunction GaN PN diodes remains inadequately explored. This work aims to fill this gap by employing Silvaco ATLAS to model the effect of uniaxial strain on GaN PN junctions. The study investigates how strain-induced polarization charges impact the electrostatic potential, depletion region, and I–V behavior, thereby contributing to improved understanding and optimization of GaN device performance. 2. Methodology A one-dimensional GaN PN junction was modeled using Silvaco ATLAS. The structure consists of: • n-type GaN: thickness = 2 µm, donor concentration ND=1×1018 cm−3 • p-type GaN: thickness = 1 µm, acceptor concentration NA=1×1017 cm−3 The default GaN material parameters used were: bandgap Eg=3.4 eV, dielectric constant εr=9.5, and electron affinity χ=4.1 eV. Mechanical strain (ε) was applied in the range of −0.5% (compressive) to +0.5% (tensile). The strain-induced piezoelectric polarization charge (Ppz ) was calculated as: Ppz=e33εzz+2e31εxx where e33=0.73 C/m2 and e31=−0.49 C/m2. This additional polarization term was introduced in ATLAS using the POLARIZATION model. The following physical models were activated: ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-11 251 • Fermi – Fermi-Dirac statistics for accurate carrier density under high doping • CONMOB – concentration-dependent mobility • BANDGAP – strain-dependent bandgap correction • SRH – Shockley–Read–Hall recombination • POLARIZATION – piezoelectric and spontaneous polarization effects The bias sweep was performed from −2 V to +2 V to obtain I–V characteristics. Mesh density was refined near the junction to ensure convergence. 3. Results and Discussion Figure 1 shows the simulated energy band diagrams for unstrained and strained GaN PN junctions. Under compressive strain (−0.5%), the conduction and valence bands shift upward, increasing the built-in potential by ~0.1 eV. Conversely, tensile strain (+0.5%) reduces the built-in potential due to negative polarization charges at the junction interface. This behavior can be explained by the piezoelectric field Epz induced by strain, which either adds to or opposes the intrinsic junction field. The resulting modification in potential affects both depletion region width and carrier injection dynamics. The depletion width (W) was extracted from the electric field profiles. Under compressive strain, W increased by approximately 9%, whereas tensile strain reduced it by 7%. This variation follows the analytical relation: 𝑊=√2𝜀𝑐(𝑉𝑏𝑖−𝑉) 𝑞(1 𝑁𝐴−1 𝑁𝐷) where Vbi is modified by strain-induced polarization. The observed trends confirm that compressive strain strengthens the junction field, widening the depletion region. The I–V characteristics, shown in Figure 2, reveal a strong dependence on the applied strain. At forward bias of 1 V, the current density under tensile strain increases by ~25% compared to the unstrained case, due to reduced barrier height and enhanced carrier injection. Conversely, compressive strain reduces forward current density by ~18% as the potential barrier increases. The reverse current exhibits a minor increase under tensile strain, indicating a slightly narrower depletion region and higher tunneling probability. These effects highlight the importance of mechanical stress control in GaN device reliability. The results are consistent with the coupling between mechanical strain and piezoelectric polarization in wurtzite GaN. Strain modifies polarization charge density, which in turn alters the internal electric field and junction electrostatics. The observed sensitivity of I–V behavior to ±0.5% strain suggests ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-11 252 that even minor residual stresses from epitaxy or packaging could significantly influence GaN device performance. 4. Conclusion A detailed numerical investigation of the strain-induced effects on Gallium Nitride (GaN) PN junctions has been thoroughly performed using the Silvaco ATLAS device simulator. The computational framework incorporates both compressive and tensile strain conditions to analyze how mechanical deformation alters the electrostatic and transport properties of GaN-based diodes. Simulation results reveal that the inclusion of strain strongly influences the built-in potential, electric field distribution, and depletion width, primarily through the modification of piezoelectric polarization and band-edge alignment. Under tensile strain, the piezoelectric field partially compensates the internal potential barrier, facilitating enhanced charge carrier injection and thereby increasing the forward conduction current. Conversely, compressive strain generates additional polarization charges that intensify the built-in field, widen the depletion region, and suppress the forward current flow. This dual behavior highlights the delicate balance between mechanical and electrostatic effects governing carrier dynamics in wide-bandgap semiconductors. Furthermore, quantitative analysis demonstrates that even small strains (±0.5%) can lead to measurable variations in current density and junction potential, emphasizing the need for precise strain control during epitaxial growth and device packaging. The results obtained from this study underscore the crucial role of strain engineering as a viable strategy for performance optimization in GaN-based power electronics and optoelectronic devices. Adjusting strain parameters can effectively tailor junction properties, improve efficiency, and enhance overall device reliability. Future research should extend this modeling framework by incorporating temperature-dependent effects, anisotropic strain tensors, and defect-induced polarization variations to capture a more comprehensive picture of the coupled electromechanical phenomena in III-nitride materials. In addition, experimental validation through Raman spectroscopy, X-ray diffraction, and current– voltage measurements on strained GaN diodes will be essential to corroborate the simulation outcomes. Ultimately, this work provides both theoretical and practical insights into the interplay between strain, polarization, and carrier transport, paving the way for next-generation GaN-based device design and reliability enhancement. REFERENCES 1. 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