【International Papers】Electrical conductivity, luminescence, and deep acceptor levels in β-Ga₂O₃-In₂O₃ polycrystalline solid solution doped with Zr⁴⁺ or Ca²⁺ ions

      Researchers from the Ivan Franko National University of Lviv have published a dissertation titled "Electrical conductivity, luminescence, and deep acceptor levels in β-Ga₂O₃-In₂O₃ polycrystalline solid solution doped with Zr⁴⁺ or Ca²⁺ ions " in Journal of Vacuum Science & Technology A.

ABSTRACT

      Photoluminescence, luminescence excitation spectra, and electrical conductivity of β-Ga₂O₃-In₂O₃ solid solutions were studied. For this purpose, polycrystalline samples of unintentionally doped (UID) and doped with Ca or Zr β-Ga₂O₃-In₂O₃ solid solution with 20% In were synthesized and characterized. All samples were obtained by the high-temperature solid-phase method from appropriate oxides at 1300 °C at low and high oxygen partial pressure. It was established that UID and doped with Ca²⁺ or Zr⁴⁺ samples synthesized in an oxygen atmosphere were highly resistive, while the samples synthesized in an argon atmosphere had high conductivity. The conductivity was the lowest in the samples doped with Ca²⁺ and was 10⁻¹³ Ω⁻¹ cm⁻¹, while in the samples doped with Zr⁴⁺, the electrical conductivity was the highest and reached 10⁻³ Ω⁻¹ cm⁻¹. The broadband luminescence of β-Ga₂O₃-In₂O₃ solid solution is a superposition of three elementary bands with maxima in the violet 3.08 eV, blue 2.73 eV, and green 2.45 eV regions of the spectrum. Doping with Ca²⁺ or Zr⁴⁺ impurities and varying the synthesis atmosphere led mainly to a redistribution of intensities between the elementary luminescence bands. The luminescence arises from the radiative recombination of charge carriers through donor–acceptor pairs and self-localized holes. Donors and acceptors are formed by native defects such as (Ga_i, V_Ga, V_GaV_o) or doping impurities (Zr⁴⁺, Ca²⁺). Unlike the luminescence spectra, the luminescence excitation spectra change significantly when the synthesis conditions vary or when doping with divalent impurities. The excitation band at 4.46 eV is due to electron transitions from the V_Ga or V_GaV_O acceptor levels to the conduction band. Electron transitions from acceptor levels of Ca²⁺ impurities are manifested in the intense excitation band at 4.1 eV.

FIG. 1.Luminescence spectrum of UID β-(Ga_0.8In_0.2)₂O₃ [(a)–(c)], β-(Ga_0.8In_0.2)₂O₃:Zr ceramics [(d)–(f)], and β-(Ga_0.8In_0.2)₂O₃:Ca [(g)–(i)] ceramics synthesized in oxygen [(a), (d), and (g)] and argon [(b), (e), and (h)], and the normalized difference spectrum of luminescence for samples synthesized in an oxygen and argon atmospheres [(c), (f), and (i)].

FIG. 2. Photoluminescence excitation spectra of elementary emission bands of the UID β-(Ga_0.8In_0.2)₂O₃ ceramics synthesized in oxygen (a) and argon (b) atmospheres. The shaded Gaussians that illustrate the computer approximation of the excitation spectrum [(c) and (d)] and a schematic image of the emission corresponding to the spectral range for which the excitation spectra were recorded.

Original link:https://doi.org/10.1116/6.0003466