Fig. 1 The energy band diagrams of the NiO/β-Ga2O3 heterojunctions at thermal equilibrium with different β-Ga2O3 substrate orientations.




Fig. 2 Band alignments of the NiO/β-Ga2O3 heterojunctions as a function of post-deposition annealing temperature.




Fig. 3 Energy band diagrams of the NiO/β-Ga2O3 heterojunction p-n diode at a (a) low and (b) high forward bias.




Fig. 4 The milestones of the state-of-the-art NiO/β-Ga2O3 heterojunction based power devices.

Xing Lu, et al, J. Semicond. 44, 061802 (2023)
https://doi.org/10.1088/1674-4926/44/6/061802
&超宽带隙氧化镓半导体专刊文章&

(1) Ga2O3-based devices can achieve higher breakdown voltage (BV) and lower specificbon-resistance (Ron,sp) simultaneously.
(2) A bipolar structure usually possesses low leakage current, high thermal stability, and good surge handling capability, which is much preferred over the unipolar configuration for power electronics.
(3) NiO thin films can be grown by several techniques such as sol-gel spin coating, radio frequency (RF) sputtering, pulsed laser deposition (PLD), atomic layer deposition (ALD), MBE, and thermal oxidation of Ni. RF sputtering has become the optimal method for depositing NiO on β-Ga2O3.
(4) The sputtered NiO films were polycrystalline even after a post-deposition annealing (PDA) process.
(5) The crystallinity of sputtered NiO showed no strong dependency on the β-Ga2O3 substrate orientations.
(6) The band alignment of the sputtered NiO/β-Ga2O3 heterojunctions varies from each other, which could be determined by many factors, such as the strain, defects/vacancies, interfacial contamination, crystal orientation, and so on.
(7) The VBO values of the NiO/β-Ga2O3 heterojunctions were extracted to be 2.12 ± 0.06, 2.44 ± 0.07, and 2.66 ± 0.07 eV for (-201), (001) and (010) β-Ga2O3 substrates, respectively.
(8) A possible unstable performance of the NiO/β-Ga2O3 heterojunction device occur at high temperatures.
(9) When the low forward bias is <1.6 V, interface recombination has been revealed to be the dominant forward conduction mechanism of the NiO/β-Ga2O3 heterojunctions, in which the electrons and holes recombined once they meet at the heterojunction interface by overcoming the barrier of the depletion region.
(10) The electrons contributed by β-Ga2O3 recombine with the holes in the valence band of NiO through interfacial states, which forms the interface recombination current.
(11) When the forward bias increased (>1.6 V), a trap-assisted multistep tunneling model became the dominant conduction mechanism in the NiO/β-Ga2O3 heterojunction.
(12) The grain boundaries in the sputtered NiO films act as trap states and facilitate electron tunneling.
(13) When the forward bias went beyond 3.5 V, a high-level injection phenomenon and corresponding conductivity modulation effect were observed.
(14) The bottom lightly doped NiO layer of double-layer NiO film could smoothen the electric field, while the upper heavily doped NiO layer can reduce the Ron,sp by lowering the metal-to-NiO contact resistance.
(15) Ion implantation in the device periphery to form a high-resistivity region can effectively relieve the electric field crowing effect and improve the breakdown voltage in power devices.
(16) Schottky barrier diodes (SBDs) possess properties of low turn-on voltage and fast switching speed. Meanwhile, p-n diodes have the advantages of low leakage current and good surge handling capability.
(17) Pool-Frenkel (PF) emission refers to the electric-field-enhanced thermal excitation of electrons from a trapped state into a continuum of electronic states.
(18) Trap states at the NiO/β-Ga2O3 heterojunction interface can cause large hysteresis and excess reverse leakage current.