Ab- initio Calculations of the Physical Properties in Gallium Nitride at Equilibrium Phases: Rocksalt and Wurtzite

Süleyman Demirel University Journal of Natural and Applied Sciences Volume 22, Issue 1, 13-23, 2018 Süleyman Demirel Üniversitesi Fen Bilimleri Enstitüsü Dergisi Cilt 22, Sayı 1, 13-23, 2018 DOI: 10.19113/sdufbed.38099 Ab-initio Calculations of the Physical Properties in Gallium Nitride at Equilibrium Phases: Rocksalt and Wurtzite Cengiz SOYKAN*1 1Ahi Evran University, Vocational School of Health Services, 40100, Kırşehir (Alınış / Received: 24.07.2017, Kabul / Accepted: 20.10.2017, Online Yayınlanma / Published Online: 28.12.2017) Keywords Density functional theory, Ab-initio calculations, Elastic stiffness coefficients, Phase transition pressure, Mechanical properties, Electronic structure Abstract: Ab-initio total energy calculations have been performed utilizing the Density Functional Theory (DFT) inside the generalized gradient approximation (GGA) parameterized by Perdew-Burke-Ernzerhof (PBE). Interactions of the ions and electrons with each other’s was characterized via PAW potential within the valance electron configurations Ga-4s24p1 and N-2p22p3 to investigate the physical properties in the rocksalt B1 and wurtzite B4 phases. The equilibrium transition pressure (Pt) from B4 to B1 was estimated at about 33.66 GPa by using the common tangent construction. The DFT calculations indicate that the upper bands of wurtzite B4 between -0.256 eV and the Fermi level were mostly owing to N-p states. The lowest conduction bands were consisted of a mixture of N-s and Ga-s states. The valance band maximum and the conduction band minimum occured at the Γ symmetry point. Concordantly, B4 phase of GaN had a direct band gap at Γ-point, which calculated as 1.702 eV. The highest valance band of rocksalt B1 were consisted of with a major contribution of N-2p states. Although, the indirect band gap of the rocksalt B1 phase has been reported from the valance band maximum at the L-point to the conduction band minimum along the X direction [7], we observed the indirect energy band gap from the valance band maximum at the L-point to the conduction band minimum along the Γ direction. Our calculated value of indirect energy band gap for the rocksalt B1 phase was 0.777 eV and it was lower than the previous calculations. Galyum Nitrür’ün Kararlı Rocksalt ve Wurtzite Fazlarının Fiziksel Özelliklerinin Abinitio Hesabıyla Belirlenmesi Anahtar Kelimeler Yoğunluk fonksiyonel teorisi, Ab-initio Hesabı, Elastik sertlik katsayıları, Faz geçiş basıncı, Mekanik özellikler, Elektronik Yapı Özet: Perdew-Burke-Ernzerhof (PBE) tarafından parametrelize edilmiş, genelleştirilmiş eğim yaklaşımı (GGA) dahil olan Yoğunluk Fonksiyonel Teorisi (DFT) kullanılarak, ab-initio toplam enerji hesapları yapılmıştır. Rocksalt B1 ve wurtzite B4 fazlarının fiziksel özelliklerini araştırmak için PAW potansiyeli Ga-4s24p1 ve N-2p22p3 valans elektron konfigürasyonu ile iyonlar ve elektronlar arasındaki etkileşimi tanımlamak için kullanılmıştır. Ortak teğet yapımı kullanılarak, B4 yapısından B1 yapısına denge geçiş basıncı (P t) 33.66 GPa olarak hesaplanmıştır. DFT hesapları wurtzite B4’ün en üst bandlarının -0.256 eV ile Fermi seviyesi arasında çoğunlukla N-p durumlarına bağlı olduğunu ortaya koymaktadır. En düşük iletim bandı N-s ve Ga-s durumlarının bir karışımından oluşmaktadır. Valans bandının maksimumu ve iletim bandının minimumu Γ simetri noktasında meydana gelmektedir. Buna paralel olarak, GaN’ün B4 fazı Γ noktasında 1.702 eV olarak hesaplanan bir dolaysız (direkt) band aralığına sahiptir. Rocksalt B1 fazının en yüksek valans bandı başlıca N-2p durumlarının katkılarından oluşmaktadır. Rocksalt B1 fazının dolaylı (in direkt) band aralığının valans bandının en üst bölgesi L-noktasından iletim bandının en alt bölgesi X yönünde olduğu rapor edilmesine rağmen [7], biz dolaylı (in direkt) band aralığını valans bandının en üst bölgesi L noktasından iletim bandının en alt bölgesi Γ yönünde olduğunun gözlemledik. Rocksalt B1 fazı için bizim hesapladığımız dolaylı (in direkt) band aralığı değeri 0.777 eV’dir ve önceki çalışmalardan daha düşüktür. *Corresponding author: 13 C. Soykan / Ab-initio Calculations of the Physical Properties in Gallium Nitride at Equilibrium Phases: Rocksalt and Wurtzite 1. Introduction Zoroddu et al. using local and gradient-corrected density-functional theory [12]. According to this paper, AlN, GaN and InN crystal structures are nonideal with respect to both the axial ratio and the internal parameter. Deviation from ideality increases from GaN to InN to AlN. The binding energy, lattice constants and internal parameters are considerably well estimated by the GGA in the many materials and approximations [12]. In the light of the previous theoretical studies, generalized gradient approximations (GGA) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules and solids. Therefore, we preferred to use the GGA in order to be able to more specifically calculate the electronic features in our work. Gallium Nitride (GaN) is a two-component semiconductor. In recent years, it has become more popular to enormous potential fabrication of various semiconductor for high-power and frequency devices such as short wavelength or blue light emitting diodes (LEDs), laser diodes (LD), optical detectors and ultra violet (UV) photo detectors since GaN provides very high breakdown voltages and electron mobility. Besides, Gallium nitride as RF power amplifiers is also an ideal candidate for high-power and temperature microwave applications. As a conclusion, it is very important that to decide the physical properties of GaN material as accurately as possible which has various superior features. In recent years, many of the theoretical and experimental studies have been related to GaN semiconductor material. Achour et al. investigated the structural properties of GaN for different crystal structures such as NaCI, CsCI, wurtzite, zincblende, 𝛽tin, Cinnabar and NiAs by using FPLMTO method [1]. Yao et al. studied the mechanisms of the wurtziterocksalt phase transformation of GaN semiconductor by DFT based metadynamics method [2]. Also, the thermodynamics properties for B4 and B1 phases of GaN by carrying out the first-principles calculations within the DFT and DFPT were investigated by Zhou et al. [3]. Qian et al. reconstructed the solid solid phase transformations of GaN material from B4 to B1 and from B3 to B1 by applying the nudged elastic band (NEB) [4]. On the other hand, the theoretical study for the structural parameters and phase transformation for Gallium nitride under pressure up to 100 GPa pressure were reported by Saoud et al. [5]. Xiao et al. carried out the pressure-induced B4 and B3 to B1 phase transformation for AlN and GaN by using first-principle total energy calculations [6]. The physical properties of GaN semiconductor as a theoretical study were presented used the firstprinciples full-potential PAW approach implemented GGA by Arbouche et al. (...truncated)