Abstract
Systemic investigations are performed to comprehend the structural, optical, and electrical characteristics of four niobium (Nb) doped β-Ga2O3 crystals (β-Ga2O3:Nb) grown by the optical floating zone (OFZ) method. All of the β-Ga2O3:Nb crystals revealed monoclinic phases and good crystalline qualities. While the different Nb doped (i.e., 0.0001 mol%, 0.01 mol%, 0.1 mol% and 0.5 mol%) samples exhibited slightly changed bandgap energies Eg (≡ 4.72 eV, 4.73 eV, 4.81 eV, 4.68 eV)—the luminescence features indicated distinctive defect levels—affecting the electronic energy structure significantly. By increasing the Nb doping level from 0.0001 mol% to 0.1 mol%, the Fermi level (EF) moves closer to the bottom of the conduction band. For the sample with Nb doping 0.5 mol%—no further improvement is noticed in the electronic properties. Finally, the energy band diagrams of four samples are given.
Highlights
Among the five commonly identified polymorphs of the gallium oxide (Ga2 O3 )—the β-Ga2 O3 phase is the most thermodynamically stable exhibiting a monoclinic crystal structure, wider band gap, high breakdown electric field, and many other excellent properties [1,2,3,4]
There exist no systematic studies on the defect energy levels and electronic energy band structures of β-Ga2 O3 :Nb
We report the results of a systematic study on the optical characteristics and electronic energy band structures of Nb-doped β-Ga2 O3 crystals grown by the optical floating zone (OFZ) method
Summary
Among the five commonly identified polymorphs of the gallium oxide (Ga2 O3 )—the β-Ga2 O3 phase is the most thermodynamically stable (melting point of 1795 ◦ C) exhibiting a monoclinic crystal structure, wider band gap, high breakdown electric field, and many other excellent properties [1,2,3,4]. It is of great interest to improve the electric conductivity of β-Ga2 O3 by doping. It has been established that Si, Sn, and Ge are the most effective n-type dopants for β-Ga2 O3 materials [10,11,12]. Nb dopant has emerged as the best candidate for n-type doping because the atomic radius of Nb is very close to that of the Ga atom. Earlier Zhou et al [14] reported Nb doping as an effective approach to improve the resistivity and carrier density of β-Ga2 O3. We strongly feel that the outcomes described here are of vital importance for many optoelectronic device applications
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