Quang Tu Thieu

Homoepitaxial growth of β-Ga2O3 layers by halide vapor phase epitaxy

Thick high-purity β-Ga2O3 layers of high crystalline quality were grown homoepitaxially by halide vapor phase epitaxy (HVPE) using gaseous GaCl and O2 on (001) β-Ga2O3 substrates prepared by edge-defined film-fed growth. The surface morphology and structural quality of the grown layer improved with increasing growth temperature. X-ray diffraction ω-rocking curves for the (002) and (400) reflections for the layer grown at 1000 °C had small full widths at half maximum. Secondary ion mass spectrometry and electrical characteristics revealed that the growth of high-purity β-Ga2O3 layers with low effective donor concentration (Nd − Na < 1013 cm−3) is possible by HVPE.

Temperature-dependent capacitance–voltage and current–voltage characteristics of Pt/Ga2O3 (001) Schottky barrier diodes fabricated on n––Ga2O3 drift layers grown by halide vapor phase epitaxy

We investigated the temperature-dependent electrical properties of Pt/Ga2O3 Schottky barrier diodes (SBDs) fabricated on n–-Ga2O3 drift layers grown on single-crystal n+-Ga2O3 (001) substrates by halide vapor phase epitaxy. In an operating temperature range from 21 °C to 200 °C, the Pt/Ga2O3 (001) Schottky contact exhibited a zero-bias barrier height of 1.09–1.15 eV with a constant near-unity ideality factor. The current–voltage characteristics of the SBDs were well-modeled by thermionic emission in the forward regime and thermionic field emission in the reverse regime over the entire temperature range.

Ga 2 O 3 Schottky barrier diodes with n − -Ga 2 O 3 drift layers grown by HVPE

The new wide-bandgap oxide semiconductor, gallium oxide (Ga₂O₃), has gained attraction as a promising candidate for power device applications because of its excellent material properties and suitability for mass production. The Baligas figure of merit of Ga₂O₃ is expected to be much larger than those of SiC and GaN due primarily to Ga₂O₃s extremely large bandgap of 4.5~4.9 eV, which will enable Ga₂O₃ power devices with higher breakdown voltage (V_br) and efficiency than SiC and GaN devices [1]. The other important advantage of Ga₂O₃ is that large, high-quality bulk single crystals can be grown by using melt growth methods. Recently, we developed a homoepitaxial growth technique for high-purity Ga₂O₃ thin films on single-crystal Ga₂O₃ substrates by halide vapor phase epitaxy (HVPE) [2, 3]. This is the first report on Ga₂O₃ Schottky barrier diodes (SBDs) with epitaxial Si-doped n^--Ga₂O₃ drift layers grown by HVPE.

Electronic properties of the residual donor in unintentionally doped .BETA.-Ga2O3

Electron paramagnetic resonance was used to study the donor that is responsible for the n-type conductivity in unintentionally doped (UID) β-Ga2O3 substrates. We show that in as-grown materials, the donor requires high temperature annealing to be activated. In partly activated materials with the donor concentration in the 1016 cm−3 range or lower, the donor is found to behave as a negative-U center (often called a DX center) with the negative charge state DX− lying ∼16–20 meV below the neutral charge state d0 (or Ed), which is estimated to be ∼28–29 meV below the conduction band minimum. This corresponds to a donor activation energy of Ea∼44–49 meV. In fully activated materials with the donor spin density close to ∼1 × 1018 cm−3, donor electrons become delocalized, leading to the formation of impurity bands, which reduces the donor activation energy to Ea∼15–17 meV. The results clarify the electronic structure of the dominant donor in UID β-Ga2O3 and explain the large variation in the previously reported ...

Thermal stability of beta-Ga2O3 in mixed flows of H-2 and N-2

The thermal stability of β-Ga2O3(010) substrates was investigated at atmospheric pressure between 250 and 1450 °C in a flow of either N2 or a mixture of H2 and N2 using a radio-frequency induction furnace. The β-Ga2O3 surface was found to decompose at and above 1150 °C in N2, while the decomposition of β-Ga2O3 began at only 350 °C in the presence of H2. Heating β-Ga2O3 substrates in gas flows containing different molar fractions of H2 demonstrated that the decomposition was promoted by increasing the H2 molar fractions. Thermodynamic analysis showed that the dominant reactions are in N2 and in a mixed flow of H2 and N2. The second-order reaction with respect to H2 determined for the mixed flows agrees with the experimental results for the dependence of the β-Ga2O3 decomposition rates on the H2 molar fraction.

Preparation of 2-in.-diameter (001) β-Ga2O3 homoepitaxial wafers by halide vapor phase epitaxy

The homoepitaxial growth of thick β-Ga2O3 layers on 2-in.-diameter (001) wafers was demonstrated by halide vapor phase epitaxy. Growth rates of 3 to 4 µm/h were confirmed for growing intentionally Si-doped n-type layers. A homoepitaxial layer with an average thickness and carrier concentration of 10.9 µm and 2.7 × 1016 cm−3 showed standard deviations of 1.8 µm (16.5%) and 0.5 × 1016 cm−3 (19.7%), respectively. Ni Schottky barrier diodes fabricated directly on a 5.3-µm-thick homoepitaxial layer with a carrier concentration of 3.4 × 1016 cm−3 showed reasonable reverse and forward characteristics, i.e., breakdown voltages above 200 V and on-resistances of 3.8–7.7 mΩ cm2 at room temperature.

Investigation of NH3 input partial pressure for N-polarity InGaN growth on GaN substrates by tri-halide vapor phase epitaxy

The influence of NH3 input partial pressure on N-polarity InGaN grown by tri-halide vapor phase epitaxy was investigated. It was found that surface morphology, solid composition and optical propert ...

Breakdown mechanism in 1 kA/cm2 and 960 V E-mode β-Ga2O3 vertical transistors

A high current density of 1 kA/cm2 is experimentally realized in enhancement-mode Ga2O3 vertical power metal-insulator field-effect transistors with fin-shaped channels. Comparative analysis shows that the more than doubled current density over the prior art arises from a larger transistor channel width; on the other hand, a wider channel also leads to a more severe drain-induced barrier lowering therefore premature transistor breakdown at zero gate-source bias. The observation of a higher current density in a wider channel confirms that charge trapping in the gate dielectric limits the effective field-effect mobility in these transistor channels, which is about 2× smaller than the electron mobility in the Ga2O3 drift layer. The tradeoff between output-current density and breakdown voltage also depends on the trap density. With minimal trap states, the output current density should remain high while breakdown voltage increases with decreasing fin-channel width.

Demonstration of Ga 2 O 3 trench MOS-type Schottky barrier diodes

β-Ga2O3 is a suitable material for next-generation high-power devices because it has excellent material properties and mass productivity. In the past, we have demonstrated field-plated Ga2O3 Schottky barrier diodes (SBDs) with nearly ideal reverse characteristics limited mainly by the thermionic field emission (TFE) leakage current. [1] However, the TFE current, that is, leakage current, was very large because of the large electric field at the Schottky metal/semiconductor interface. Here, introducing a junction barrier controlled Schottky structure or trench MOS barrier structure is an effective way to decrease the electric field [2]. In this study, we succeeded in developing Ga2O3 trench MOS-type SBDs (MOSSBDs) for the first time and examined their characteristics.