Deep level defects in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy

Abstract

Deep level defects were characterized in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy (PAMBE) using deep level optical spectroscopy (DLOS) and deep level transient (thermal) spectroscopy (DLTS) applied to Ni/β-Ga2O3:Ge (010) Schottky diodes that displayed Schottky barrier heights of 1.50 eV. DLOS revealed states at EC − 2.00 eV, EC − 3.25 eV, and EC − 4.37 eV with concentrations on the order of 1016 cm−3, and a lower concentration level at EC − 1.27 eV. In contrast to these states within the middle and lower parts of the bandgap probed by DLOS, DLTS measurements revealed much lower concentrations of states within the upper bandgap region at EC − 0.1 – 0.2 eV and EC − 0.98 eV. There was no evidence of the commonly observed trap state at ∼EC − 0.82 eV that has been reported to dominate the DLTS spectrum in substrate materials synthesized by melt-based growth methods such as edge defined film fed growth (EFG) and Czochralski methods [Zhang et al., Appl. Phys. Lett. 108, 052105 (2016) and Irmscher et al., J. Appl. Phys. 110, 063720 (2011)]. This strong sensitivity of defect incorporation on crystal growth method and conditions is unsurprising, which for PAMBE-grown β-Ga2O3:Ge manifests as a relatively “clean” upper part of the bandgap. However, the states at ∼EC − 0.98 eV, EC − 2.00 eV, and EC − 4.37 eV are reminiscent of similar findings from these earlier results on EFG-grown materials, suggesting that possible common sources might also be present irrespective of growth method.

Electrical Properties of Vertical p‐NiO/n‐Ga2O3 and p‐ZnCo2O4/n‐Ga2O3 pn‐Heterodiodes

“…They show similar activation energies and capture cross sections. A defect level with similar activation energy was found in homoepitaxial β ‐Ga 2 O 3 thin films fabricated by metal organic chemical vapor deposition or fabricated by plasma enhanced molecular beam epitaxy . In bulk samples, a defect level with this activation energy was not detected or found by computer simulations .…”

Defect Formation Energies of Interstitial C, Si, and Ge Impurities in β‐Ga2O3

“…With a band‐gap in the range from 4.5 to 4.9 eV, a high breakdown field, and a tunable carrier concentration, β ‐Ga 2 O 3 represents an excellent candidate for deep‐UV devices, metal–oxide–semiconductor field effect transistors, and Schottky diodes . Experimentally, n‐type doping of β ‐Ga 2 O 3 has been achieved by various techniques . At variance, p‐type β ‐Ga 2 O 3 appears to be more difficult to realize, in accordance with density functional theory (DFT) studies …”

“…When the samples are intentionally doped with Si, donor concentrations around cm −3 can be achieved . Germanium impurities at concentrations of 10 17 cm −3 can be introduced in β ‐Ga 2 O 3 through intentional doping by means of various molecular beam epitaxy techniques . This impurity has the advantage of having a cationic size in very good match with Ga + compared to the commonly used Si cations.…”

“…In spite of these promising properties of doped β ‐Ga 2 O 3 , intentional or unintentional doping causes deep defect levels in the band gap, which hamper the electronic properties of the material and make its incorporation into practical devices problematic. Recent experiments reported the occurrence of a rich spectrum of defect states in the band gap of β ‐Ga 2 O 3 . In particular, while defects occurring in the vicinity of the valence band maximum are well reproduced using various experimental techniques, energy levels and trap concentrations of defects occurring in the upper part of the band gap depend on the adopted growth method .…”

“…Recent experiments reported the occurrence of a rich spectrum of defect states in the band gap of β ‐Ga 2 O 3 . In particular, while defects occurring in the vicinity of the valence band maximum are well reproduced using various experimental techniques, energy levels and trap concentrations of defects occurring in the upper part of the band gap depend on the adopted growth method . Hence, it is of interest to determine the atomistic nature of these defect states in order to design proper passivation road maps.…”