High performance NiO/β-Ga2O3 heterojunction pn diodes were realized by applying a sputtered p-type NiO film onto a lightly doped n-type β-Ga2O3 epitaxial layer. Taking advantage of the high barrier height against carriers within the pn heterojunction, the demonstrated device exhibited a high breakdown voltage (VB) of 1059 V without optimized electric field management techniques, and before breakdown the reverse leakage current density remained below 1 μA/cm2. Simultaneously, a relatively low specific on-resistance (Ron, sp) of 3.5 mΩ∙cm2 was achieved. The built-in potential of the heterojunction that determined by a capacitance-voltage (C-V) measurement was around 2.4 eV. As discussed in terms of the energy band diagram of a type-II heterojunction, the conduction band and valence band offsets at the NiO/β-Ga2O3 hetero-interface were estimated to be 1.2 and 2.3 eV, respectively.

In this study, UV-visible flexible resistivity-type photo-detectors were demonstrated with CdS-nanowires (NWs) percolation network channel and Ag-NWs percolation network electrode. The devices were fabricated on Mixed Cellulose Esters (MCE) membrane using a lithographic filtration method combined with a facile non-transfer process. The photo-detectors demonstrated strong adhesion, fast response time, fast decay time, and high photo sensitivity. The high performance could be attributed to the high quality single crystalline CdS-NWs, encapsulation of NWs in MCE matrix and excellent interconnection of the NWs. Furthermore, the sensing performance was maintained even the device was bent at an angle of 90°. This research may pave the way for the facile fabrication of flexible photo-detectors with high performances.

This work presents the fabrication and characterization of a high-performance vertical Nickel oxide (NiO)/Beta gallium oxide ( β-Ga ₂ O ₃ ) heterojunction p-n diode. The heterojunction was fabricated by sputtering a p-NiO thin film onto an epitaxial n ^- - β-Ga ₂ O ₃ drift layer. The sputtered NiO, revealed to be polycrystalline, showed an improved crystallinity after annealed in an oxygen ambient, while a seamless contact with the underneath single crystalline β-Ga ₂ O ₃ was observed. A high hole concentration of 1- 3×10 ¹⁹ cm ^-3 and an improved Ohmic contact were also obtained by the annealing process, as confirmed by the Hall and TLM measurements, respectively. A high breakdown voltage ( V _B ) of 1.4 kV and a low specific ON-resistance ( R _on,sp ) of 2.7 mΩ·cm ² were simultaneously achieved for the fabricated diodes, yielding a superior Baliga's figure-of-merit (BFoM) of 0.73 GW/cm ² . From the temperature-dependent current-voltage ( I- V) measurements, two carrier transport mechanisms, namely interface recombination and multistep tunneling, have been identified in the forward conduction of the NiO/ β-Ga ₂ O ₃ heterojunction. The fast recovery property of the device, which was revealed by a double-pulse test, further confirmed the purposed carrier transport mechanisms.

This work presents the optimization of a NiO/ $\beta $ -Ga2O3 heterojunction diode (HJD) by adjusting the structural parameters of the NiO layer. A rapid thermal annealing (RTA) process was utilized to modulate the hole concentration of the sputtered NiO. The influence of the NiO layer geometry and its hole concentration on the HJDs’ electrical properties has been thoroughly investigated and discussed based on both the experimental study and the technology computer-aided design (TCAD) simulation. It was found that the forward current of the HJDs was mainly determined by the size of the anode electrode regardless of the NiO layer dimension, indicating the poor current spreading within the NiO film. Enlarging the NiO layer dimension with a fixed anode or adjusting the hole concentration to an optimal value could benefit the device breakdown voltage ( ${V}_{B}$ ) by reducing the electric field crowding effect. An optimum value of ${\sim }2\,\, {}\times {} 10^{17}$ cm−3 was determined for the HJDs with a drift layer doping concentration of $1.8\,\, {}\times {}10^{16}$ cm−3. To achieve a good balance between ${V}_{B}$ and the specific ON-resistance ( ${R}_{{\mathrm {ON,sp}}}$ ), a double-layer structure ( $\text{p}^{+}$ NiO/ $\text{p}^{-}$ NiO) was adopted and optimized, yielding a greatly enhanced performance in the NiO/ $\beta $ -Ga2O3 HJDs. The results provided a useful insight into the $\text{p}^{-}$ NiO-related $\beta $ -Ga2O3 power device design.