Electrical and optical properties of Zr doped β-Ga₂O₃ single crystals

Abstract

Sn and Si are the typical dopants for achieving tunable n-type conductivity of β-Ga2O3 single crystals grown from the melt. Here, we explore Zr doping in β-Ga2O3 as assessed with UV–vis-NIR, Hall Effect, I–V, and CV measurements and hybrid functional calculations. Single crystals were grown from the melt with nominal Zr doping between 0.1 and 0.5 at% using Czochralski and vertical gradient freeze methods in Ar + O2. Our results suggest that ZrGa behaves as a shallow donor, with a measured activation energy of ∼10 meV. Our samples show an electron mobility ∼73–112 cm2 V−1 s−1, resistivity ∼0.08–0.01 ohm cm, and carrier density of n = 6.5 × 1017−5 × 1018 cm3 at room temperature.

Experimental Hall electron mobility of bulk single crystals of transparent semiconducting oxides

“…Although solid conclusions were drawn in some cases, ambiguity in other cases remain. For instance, the electrical conductivity in β-Ga 2 O 3 may arises from solid impurities present in the starting material/intentional doping (Si, Sn, Ge, Zr, Hf) and hydrogen [48,[63][64][65][66][67][68]; in In 2 O 3 from impurities/intentional doping (Sn, Ti, Zr), fluorine, hydrogen, and possible oxygen vacancies [69][70][71][72]; in ZnO from impurities/intentional doping (such as Al, Ga, In, Sc), Zn interstitials, hydrogen, complexes [73][74][75][76]; in SnO 2 from solid impurities/intentional doping (such as Sb, As), fluorine, hydrogen [77][78][79][80]; in BaSnO 3 from intentional doping (La, Y, Pr, Nd, Sb), fluorine, and hydrogen [81][82][83][84]. Here we point out that the growth of bulk TSO single crystals at very high temperatures combined with high thermal instability (decomposition) might generate structural and intrinsic point defects that influence electrical properties to some extent.…”

Degenerate doping in β-Ga2O3 single crystals through Hf-doping

“…To theoretically assess the solubility and electrical behavior expected for Hf incorporated as a function of growth and doping conditions, we computed the defect formation energies (E f ) within a supercell approach, as previously performed to assess Zr dopants [25]. We adopt the exact same computational procedure as in [24,26,27], where all defects were modeled within 160-atom supercell representations of bulk β-Ga2O3, and total energies were computed using the Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE06) as implemented in the VASP code [28][29][30]. The atomic potentials were treated within projector-augmented wave (PAW) [31] approach and included the 4s 2 3d 10 4p 1 (Ga), 3p 6 4s 2 3d 2 (Ti), 4s 2 4p 6 5s 2 4d 2 (Zr), and 5p 6 6s 2 5d 2 (Hf) orbitals as valence electrons.…”

Schottky Barrier Height Engineering inβ-Ga2O3Using SiO2Interlayer Dielectric

“…The 5 mm × 5 mm × 0.6 mm edge-defined film-fed grown (EFG) Sn-doped (010) and (-201) β-Ga 2 O 3 substrates were acquired from Novel Crystal Tech (Japan). The Zr-doped (100) β-Ga 2 O 3 single crystal bulk substrates were grown by vertical gradient freeze (VGF) method and the details are available in reference [39]. The (100)-oriented samples were prepared by sawing first and then cleaving along the cleavage plane (100) into samples of 3.5 × 4.5 × 0.6 mm 3 dimensions and the substrate orientation was confirmed by XRD measurements and reported elsewhere [39].…”

“…The Zr-doped (100) β-Ga 2 O 3 single crystal bulk substrates were grown by vertical gradient freeze (VGF) method and the details are available in reference [39]. The (100)-oriented samples were prepared by sawing first and then cleaving along the cleavage plane (100) into samples of 3.5 × 4.5 × 0.6 mm 3 dimensions and the substrate orientation was confirmed by XRD measurements and reported elsewhere [39]. On (010) oriented substrates, the electron concentration and mobility from Hall measurements were measured to be 1.1×10 18 cm −3 and 89 cm 2 /Vs, respectively.…”