【International Papers】Assessment of Trapping Phenomena in As-Grown and Thermally-Treated Si-Doped κ-Ga₂O₃ Layers via Optical Admittance Spectroscopy

      Researchers from the University of Parma have published a dissertation titled "Assessment of Trapping Phenomena in As-Grown and Thermally-Treated Si-Doped κ-Ga₂O₃ Layers via Optical Admittance Spectroscopy" in Advanced Electronic Materials.

Background

      Gallium oxide (Ga₂O₃) is an ultra-wide bandgap semiconductor that emerged as a promising functional material in a wide range of applications, from high-power and high-frequency electronics to deep-UV detection. Many figures of merit regarding the device performance scale non-linearly with bandgap, which puts Ga₂O₃ in a prominent position compared to the wide-bandgap semiconductors (WBGs). This sesquioxide possesses some appealing properties, including a high breakdown field, large Baliga's figure of merit, high switching rate, low on-resistance, controllable n-type doping, and availability of native wafers from the melt growth technique. Five different polymorphs of this material system are known: α, β, γ, δ, κ (previously denoted as ɛ). The monoclinic β-Ga₂O₃ is the thermodynamically stable phase, which received more attention than other polymorphs. Nonetheless, this polymorph suffers from low structural symmetry associated with the monoclinic crystal structure and a strong tendency to cleavage along the (100) and (001) planes. 

Abstract

      The impact of thermal treatments on the trapping phenomena in (001) Si-doped κ-Ga₂O₃ epi-layers, via optical admittance spectroscopy technique, is reported. Two Pt/κ-Ga₂O₃ Schottky contacts are investigated: one made on top of an as-grown Si-doped κ-Ga₂O₃ layer and the other on a thermally treated one. Three different illumination conditions, including monochromatic UV-C (λ = 254 nm), UV-B (λ = 312 nm), and UV-A (λ = 365 nm), are employed for the capacitance–voltage (C–V) measurements at different bias and AC frequencies to investigate traps and deep levels in κ-Ga₂O₃:Si. The net donor density profiles in dark and approximate density of photoionized traps of the as-grown and thermally treated samples are extracted from the C–V curves in the dual-frequency mode under different illumination conditions. A SnO/κ-Ga₂O₃ p-n heterojunction, where the κ-Ga₂O₃:Si layer underwent a double thermal treatment, is also investigated to better understand the relation between thermal treatment and distribution of trap density. The transient photocapacitance and photocurrent measurements are performed under the same illumination conditions to evaluate the response times of traps. This study provides a better understanding of the trapping phenomena in the as-grown and thermally treated κ-Ga₂O₃:Si epi-layers, which are important for UV-C detection applications.