Band alignment of p-type oxide/ε-Ga₂O₃ heterojunctions investigated by x-ray photoelectron spectroscopy*

Abstract

The ε-Ga2O3 p–n heterojunctions (HJ) have been demonstrated using typical p-type oxide semiconductors (NiO or SnO). The ε-Ga2O3 thin film was heteroepitaxial grown by metal organic chemical vapor deposition (MOCVD) with three-step growth method. The polycrystalline SnO and NiO thin films were deposited on the ε-Ga2O3 thin film by electron-beam evaporation and thermal oxidation, respectively. The valence band offsets (VBO) were determined by x-ray photoelectron spectroscopy (XPS) to be 2.17 eV at SnO/ε-Ga2O3 and 1.7 eV at NiO/ε-Ga2O3. Considering the bandgaps determined by ultraviolet-visible spectroscopy, the conduction band offsets (CBO) of 0.11 eV at SnO/ε-Ga2O3 and 0.44 eV at NiO/ε-Ga2O3 were obtained. The type-II band diagrams have been drawn for both p–n HJs. The results are useful to understand the electronic structures at the ε-Ga2O3 p–n HJ interface, and design optoelectronic devices based on ε-Ga2O3 with novel functionality and improved performance.

Comprehensive Study on Ultra-Wide Band Gap La2O3/ε-Ga2O3 p–n Heterojunction Self-Powered Deep-UV Photodiodes for Flame Sensing

“…Gallium oxide (Ga 2 O 3 ) is currently one of the most popular materials used for fabricating SBPDs due to its ultrawide band gap ( E g ) (4.5–5.3 eV, which corresponds exactly to solar-blind region) and high chemical and thermal stability. To date, a lot of research and improvement work has been done on Ga 2 O 3 p–n junction-based SBPDs. − Since Ga 2 O 3 is an intrinsic n-type semiconductor and p-type doping is difficult to achieve, it is necessary for Ga 2 O 3 to form heterojunctions with other materials to prepare p–n junctions. Lanthanum oxide (La 2 O 3 ) is considered a relatively low-cost rare earth oxide with a large E g , high dielectric constant and good thermal stability. − It has been used in various applications such as gas sensors, optoelectronic devices, batteries, catalysts, supercapacitors, superconductors, light emitting diodes, laser crystals, biosensors, etc. − Furthermore, La 2 O 3 exhibits p-type semiconductivity and an ultrawide-band gap type-II heterojunction that allows for better carrier separation and transportation can be formed with Ga 2 O 3 based on the band alignment. , …”

Influence of Oxygen on Ga2O3 Deposition at Low Temperature by MOCVD

“…In recent years, as an emerging ultrawide-bandgap semiconductor, Ga 2 O 3 has received much attention from researchers, with the advantages of the substantial bandgap ranging from 4.4 to 4.9 eV , and elevated breakdown voltage, excellent optical properties, and high radiation resistance, which has been widely applied in photodiode, field-effect transistors, Schottky barrier diodes, and solar-blind photodetector . Ga 2 O 3 exhibits five distinct crystal structures, denoted as α-, β-, γ-, δ-, and ε-Ga 2 O 3.…”

Effects of preparation parameters on growth and properties of β-Ga2O3 film

“…The crystal structures of Ga 2 O 3 , including α, β , γ, δ , and ε, could transform into each other under given conditions. [17] Among them, defects in the growth of β -Ga 2 O 3 thin film include V O (oxygen vacancy), O i (oxygen interstitial), V Ga (gallium vacancy), and Ga i (gallium interstitial) due to a monoclinic crystal with the C2/m space group. Owing to the V O and Ga i with the lower formation energy, [18] β -Ga 2 O 3 is prone to forming oxygen vacancies and gallium interstitial during growth.…”