Silane-Mediated Expansion of Domains in Si-Doped κ-Ga2O3 Epitaxy and its Impact on the In-Plane Electronic Conduction

Unintentionally doped (001)-oriented orthorhombic κ-Ga2O3 epitaxial films on c-plane sapphire substrates are characterized by the presence of ≈ 10 nm wide columnar rotational domains that can severely inhibit in-plane electronic conduction. Comparing the in- and out-of-plane resistance on well-defined sample geometries, it is experimentally proved that the in-plane resistivity is at least ten times higher than the out-of-plane one. The introduction of silane during metal-organic vapor phase epitaxial growth not only allows for n-type Si extrinsic doping, but also results in the increase of more than one order of magnitude in the domain size (up to ≈ 300 nm) and mobility (highest µ ≈ 10 cm2V−1s−1, with corresponding lowest ρ ≈ 0.2 Ωcm). To qualitatively compare the mean domain dimension in κ-Ga2O3 epitaxial films, non-destructive experimental procedures are provided based on X-ray diffraction and Raman spectroscopy. The results of this study pave the way to significantly improved in-plane conduction in κ-Ga2O3 and its possible breakthrough in new generation electronics. The set of cross-linked experimental techniques and corresponding interpretation here proposed can apply to a wide range of material systems that suffer/benefit from domain-related functional properties

A Metal-Oxide Contact to ε-Ga2O3 Epitaxial Films and Relevant Conduction Mechanism

In this work, the conduction mechanisms across novel contacts to epitaxial films of pure phase epsilon-Ga2O3 (ε-Ga2O3) were investigated. Different structures made by sputtered metal and oxide thin films were tested as electrical contacts. I-V characteristics show heterogeneous behaviors, revealing different conduction mechanisms according to the applied bias. The results are interesting as they offer a viable method to obtain ohmic contacts on ε-Ga2O3, which is less studied than other gallium oxide polymorphs but may find application in new electronic and optoelectronic devices. The newly developed ohmic contacts allow to fabricate simple test devices and assess the potential of this material

Interfacial Properties of the SnO/κ-Ga2O3 p-n Heterojunction: A Case of Subsurface Doping Density Reduction via Thermal Treatment in κ-Ga2O3

: The interfacial properties of a planar SnO/κ-Ga2O3 p-n heterojunction have been investigated by capacitance-voltage (C-V) measurements following a methodological approach that allows consideration of significant combined series resistance and parallel leakage effects. Single-frequency measurements were carried out in both series- and parallel-model measurement configurations and then compared to the dual-frequency approach, which permits us to evaluate the depletion capacitance of diode independently of leakage conductance and series resistance. It was found that in the bias region, where the dissipation factor was low enough, they give the same results and provide reliable experimental C-V data. The doping profile extracted from the C-V data shows a nonuniformity at the junction interface that was attributed to a depletion of subsurface net donors at the n-side of the diode. This attribution was corroborated by doping profiles and carrier distributions in the n and p sides of the heterojunction obtained from the simulation of the measured C-V data by the Synopsys Sentaurus-TCAD suite. Hall effect measurements and Hg-probe C-V investigation on single κ-Ga2O3 layers, either as-grown or submitted to thermal treatments, support the hypothesis of the subsurface donor reduction during the SnO deposition. This study can shed light on the subsurface doping density variation in κ-Ga2O3 due to high-temperature treatment. The investigation of the SnO/κ-Ga2O3 heterointerface provides useful hints for the fabrication of diodes based on κ-Ga2O3. The methodological approach presented here is of general interest for reliable characterization of planar diodes

n-Type Doping of ε-Ga2O3 Epilayers by High-Temperature Tin Diffusion

The good control of the n-type doping is a key issue for the fabrication of efficient devices based on ε-Ga2O3 epilayers. In this work we studied the possibility of doping the ε-Ga2O3 thin films, epitaxially grown on c-oriented sapphire by metal-organic chemical vapor deposition, by means of a post-deposition treatment. For the first time, the n-type doping was achieved by depositing a tin-rich SnO2 film on top of the ε-Ga2O3 layer and keeping this bi-layer system for 4 h at a temperature of 600 °C in an evacuated furnace. The diffusion of Sn atoms into the ε-Ga2O3 film is evidenced by time-of-flight secondary-ion mass spectrometry depth profiles. Room-temperature resistivity of the order of 1 Ω•cm is obtained and the electrical characterization revealed a conduction mechanism based on variable range hopping, according to the Mott's model

Interfacial Properties of the SnO/κ-Ga₂O₃p-n Heterojunction A Case of Subsurface Doping Density Reduction via Thermal Treatment in κ‑Ga₂O₃

The interfacial properties of a planar SnO/κ-Ga2O3 p–n heterojunction have been investigated by capacitance–voltage (C–V) measurements following a methodological approach that allows consideration of significant combined series resistance and parallel leakage effects. Single-frequency measurements were carried out in both series- and parallel-model measurement configurations and then compared to the dual-frequency approach, which permits us to evaluate the depletion capacitance of diode independently of leakage conductance and series resistance. It was found that in the bias region, where the dissipation factor was low enough, they give the same results and provide reliable experimental C–V data. The doping profile extracted from the C–V data shows a nonuniformity at the junction interface that was attributed to a depletion of subsurface net donors at the n-side of the diode. This attribution was corroborated by doping profiles and carrier distributions in the n and p sides of the heterojunction obtained from the simulation of the measured C–V data by the Synopsys Sentaurus-TCAD suite. Hall effect measurements and Hg-probe C–V investigation on single κ-Ga2O3 layers, either as-grown or submitted to thermal treatments, support the hypothesis of the subsurface donor reduction during the SnO deposition. This study can shed light on the subsurface doping density variation in κ-Ga2O3 due to high-temperature treatment. The investigation of the SnO/κ-Ga2O3 heterointerface provides useful hints for the fabrication of diodes based on κ-Ga2O3. The methodological approach presented here is of general interest for reliable characterization of planar diodes