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. 2021 Oct 19;6(43):29149–29156. doi: 10.1021/acsomega.1c04380

Role of Interfacial Oxide in the Preferred Orientation of Ga2O3 on Si for Deep Ultraviolet Photodetectors

Chao-Chun Yen †, Tsun-Min Huang †, Po-Wei Chen †, Kai-Ping Chang †, Wan-Yu Wu ‡, Dong-Sing Wuu †,§,∥,⊥,*
PMCID: PMC8567405  PMID: 34746603

Abstract

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It is generally known that a layer of amorphous silicon oxide (SiO2) naturally exists on the surface of silicon, resulting in the growth of gallium oxide (Ga2O3) that is no longer affected by substrate crystallinity during sputtering. This work highlights the formation energy between the native amorphous nano-oxide film formed on the Si substrate and monoclinic β-Ga2O3 dominating the preferred orientation prepared for deep ultraviolet photodetectors. The latter were deposited on p-type silicon (p-Si) with (111) orientation using radio frequency sputtering at 600 °C and post rapid thermal annealing (RTA). The X-ray diffraction (XRD) results indicate both as-deposited and postannealing films with the (400) preferred orientation for a layer thickness of 100 nm. However, slight random orientation with the amorphous structure is mixed in the preferred one for the as-deposited film with a thickness of 200 nm and reduced after being annealed at 800 °C, which is observed by XRD and transmission electron microscopy. Meanwhile, thermal-induced massive twin boundaries (TBs) and stacking faults (SFs) were generated when annealed at 1000 °C, owing to the relaxation of lattice strain by the coherent interface. The interfacial bonding energy per unit area (Ei) between β-Ga2O3 films with various facets ((001), (010), (100), and (2̅01)) and amorphous SiO2 was calculated using density functional theory. The Ei of β-Ga2O3 (100)/SiO2 reveals the highest value (0.289 eV/Å2), which is consistent with the (100) preferred orientation of deposited films. The (100) preferred orientation is the driving force for TBs and SFs. The discrimination of responsivities and the photo/dark current contrast ratio (Iph/Idark) are inversely proportional to the amorphous structure, grain boundaries, TBs, and SFs. Therefore, optimum metal–semiconductor–metal photodetector performance is achieved for RTA-treated samples at 800 °C with an Iph/Idark of 3.91 × 102 and a responsivity of 0.702 A/W (λpeak = 230 nm) at 5 V bias for a 200 nm thin film.

1. Introduction

To accommodate the recent development of deep ultraviolet (DUV) photodetectors (PDs), which require materials having shorter cutoff wavelengths, wide-band-gap materials such as AlN, AlGaN, BN, ZnMgO, diamond, and gallium oxide (Ga2O3) thin films have been investigated.1−6 These materials have a large band gap, high breakdown electric field strength, fast saturated electron drift speed, high thermal conductivity, small dielectric constant, strong radiation resistance, and good chemical stability. Among these wide-band-gap materials, Ga2O3 is a promising oxide semiconductor because of its high breakdown voltage (approximately 8 MV/cm) and wide band gap (approximately 4.9 eV).7−10 Ga2O3 is a polymorphic material that has five phases, including α, β, γ, ε, and δ. Monoclinic β-phase gallium oxide (β-Ga2O3) has the highest chemical and physical stability11 and is thus suitable for developing antiradiation, high-frequency, high-power, and high-density integrated semiconductor devices.

Due to their wide band gap and high stability, β-Ga2O3-based heterostructures have been widely investigated as DUV PDs and light-emitting devices, such as β-Ga2O3/GaN, β-Ga2O3/SiC, β-Ga2O3/sapphire, and β-Ga2O3/Si.12−19 Of these, β-Ga2O3/Si is especially attractive because of the well-known advantages of Si substrates, including high stability, low cost, abundance, prominent application in Si-based optoelectronic integrated circuits,20−22 and especially for the amount of device array on a silicon wafer (12 inches for now). Further, as the thermal conductivity of Si (150 W/(m K))23 is greater than that of Ga2O3 (8.8 ± 3.4 W/(m K)),24 heat dissipates more efficiently for high-power devices.

Several growth techniques for Ga2O3 thin films have been proposed, including sol–gel methods,25 molecular beam epitaxy,26 metalorganic chemical vapor deposition,27−30 atomic layer deposition,31,32 pulsed laser deposition,33 magnetron sputtering,34 chemical bath deposition,35 and halide vapor-phase epitaxy.36 Although sputtering is one of the most practical ways to achieve uniformity over a large area for ceramic thin films, the resulting structure is typically amorphous or nanocrystalline, which is disadvantageous for optoelectronic properties. Therefore, a postannealing treatment is necessary to improve the film quality.37

However, Choi et al. showed that the microstructure of a β-Ga2O3 thin film with (100) preferred orientation had a twin structure on an amorphous SiO2/Si substrate during high-temperature annealing.38 The SiO2/Si substrate eliminates the influence of substrate crystallinity during the growth of the β-Ga2O3 thin film. Additionally, Wanger et al. demonstrated that layers grown on substrates of (100) orientation suffered from a high density of twins and stacking faults at a growth temperature of 850 °C.28 These defects are detrimental to electrical properties because they compensate for n-type doping, reduce carrier mobility, and eventually cause the mobility to collapse below a critical doping density.39 It is generally known that a layer of amorphous silicon oxide naturally exists on the surface of silicon, resulting in the growth of Ga2O3 that is no longer affected by substrate crystallinity during sputtering. It is therefore necessary to clarify the roles the interfacial oxide of a Si substrate and annealing treatment have on the crystallinity of Ga2O3. Besides, the effects of interfacial oxide on the preferred orientation of β-Ga2O3 on Si for the optoelectrical performance of PDs have been rarely reported.

2. Results and Discussion

To realize thermal-induced interdiffusion in sputtered Ga2O3 films, glow discharge optical emission spectroscopy (GDOES) was used to acquire elemental distribution from the film to the substrate through depth profiling. The qualitative GDOES in-depth profiles for sputtered Ga2O3 films with various thermal treatment conditions are shown in Figure 1. According to the element concentration distribution, the profiles can be divided into three regions: the film region (Rf), the concentration gradient region (Rg), and the substrate region (Rs). After rapid thermal annealing (RTA) treatments, the element concentration distribution in samples remained unchanged even after being annealed at 1000 °C. There is no obvious interdiffusion of Ga and Si, unlike our previous study on the interdiffusion of Ga and Al for the Ga2O3/sapphire heterostructure.40

Figure 1.

Figure 1

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Glow discharge optical emission spectroscopy analyses for 100 nm of as-deposited Ga2O3 samples thermally treated by RTA processes at 800, 900, and 1000 °C. The yellow, light blue, and purple background colors represent the film region (Rf), the concentration gradient region (Rg), and the substrate region (Rs), respectively.

X-ray diffraction (XRD) analyses were performed to reveal the crystallinity of the annealed β-Ga2O3 films. The resulting XRD θ–2θ scans of the as-deposited Ga2O3 samples thermally treated by RTA processes at various temperatures ranging from 700 to 1000 °C are shown in Figure 2a,b (thicknesses of 100 and 200 nm, respectively). In the 100 nm Ga2O3 film, all of the samples possessed (400) preferred orientations, which belong to β-Ga2O3. In the 200 nm sample, the diffraction peaks of (002) and (1̅11) were present, indicating that the top layer of the film (over 100 nm) was no longer aligned with the preferred orientation (400) at 600 °C (as-deposited), 700 and 800 °C. At annealing temperatures of 900 and 1000 °C, these diffraction peaks dramatically shifted toward the left, resulting in (110) and (4̅01) facets, respectively. This peak shifting was caused by twinning or stacking faults (SFs) with the top layer of the film, which is discussed later during transmission electron microscopy (TEM) analysis. In contrast, the 100 nm Ga2O3 film did not show the peak shift or other peaks present due to the (100) preferred facet after twinning, which was the same as Wanger et al.’s results.28

Figure 2.

Figure 2

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X-ray diffraction (XRD) θ–2θ scans of (a) 100 nm and (b) 200 nm thick as-deposited Ga2O3 samples treated by rapid thermal annealing (RTA) at temperatures ranging from 700 to 1000 °C.

The cross-sectional TEM images and selected area electron diffraction (SAED) patterns of the as-deposited and 800 °C RTA-treated films are shown in Figure 3. The as-deposited β-Ga2O3 film showed a combination of polycrystalline and amorphous structures, confirmed by the diffused rings of the SAED pattern, as shown in Figure 3a. In contrast, the diffraction pattern of the 800 °C RTA-treated film reveals brighter spots without the diffused ring, indicating the reduced amorphous structure and grain growth, as shown in Figure 3b.

Figure 3.

Figure 3

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Cross-sectional transmission electron microscopy (TEM) images of the 200 nm Ga2O3 thin film (a) as-deposited and (b) after RTA at 800 °C. Insets in the upper left corner indicate the selected area electron diffraction (SAED) patterns of the same sample from the area designated by white circles.

After RTA treatment at 1000 °C, low magnifications of bright-field (BF) and dark-field (DF) cross-sectional TEM images illuminate the massive twin boundaries (TBs) and SFs in the β-Ga2O3 films, as shown in Figure 4a,b. The inset SAED patterns also confirm the twin structure. The TBs along the (100) facets, which are perpendicular to the specimen, are shown in the high-resolution image presented in Figure 4c. The (200) preferred facets and SFs are parallel to the interface, as shown in Figure 4d. In complete agreement with Gao et al.’s studies,41 these showed high-density SFs along the (200) lattice planes. Overall, these results illustrate that the thermal energy induces massive TBs and SFs in β-Ga2O3 films for the (100) preferred orientation. These findings are consistent with those by Wagner et al.28 and Schewski et al.,42 who demonstrated that layers grown on the (100) orientation suffer from a high density of twins and SFs, owing to the relaxation of lattice strain. In contrast, high-resolution TEM imaging of sputtered β-Ga2O3 (2̅01)/sapphire under RTA treatment at 1000 °C in prior studies did not show massive TBs and SFs.40 The (100) preferred orientation is the driving force of TBs and SFs. Therefore, as long as the thermal annealing temperature is high enough to rearrange the local atoms on the (100) facets, the lattice strain resulting from the coherent interface between SiO2 and β-Ga2O3 (100) can be released by forming twins and SFs.

Figure 4.

Figure 4

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Twins and stacking faults formed in the 200 nm Ga2O3 film during RTA at 1000 °C, visible via low magnifications of (a) bright-field (BF) and (b) dark-field (DF) cross-sectional TEM images of Ga2O3/SiO2/p-Si. Insets show the SAED patterns of the twins. High-resolution TEM images of (c) twins and (d) the preferred orientation and stacking faults (fast Fourier transformed TEM lattice image) derived from their respective white squares indicated in (a).

Although Schewski et al. and Mazzolini et al. showed that the sequence of surface free energy is (010) > (001) > (2̅01) > (100),43,44 the effect of the substrate on the preferred orientation has not been considered. Therefore, to understand the impact of interfacial oxide on the Ga2O3 thin film, the interfacial bonding energy between various β-Ga2O3 facets and amorphous SiO2 was examined using density functional theory (DFT). As detailed in Table 1, the resulting interfacial bonding energy per unit area was 0.289 (β-Ga2O3 (100)/SiO2) > 0.280 (β-Ga2O3 (001)/SiO2) > 0.245 (β-Ga2O3 (2̅01)/SiO2) > 0.126 eV/Å2 (β-Ga2O3 (010)/SiO2). Thus, the (100) orientation is the most stable facet for the heterostructure without the influence of substrate crystallinity. These results are in accordance with Choi et al.’s results38 and the above XRD results, where the β-Ga2O3 thin film grows in (100) preferred orientation on amorphous SiO2, also indicating that interfacial oxide plays an important role during the epitaxy of β-Ga2O3 on a Si substrate. Additionally, the most striking result to emerge from the data is that just a few layers of SiO2 (about 10 Å) can affect the preferred orientation.

Table 1. Interfacial Bonding Energy of the Heterostructure per Unit Area (Ei) for (a) (001), (b) (010), (c) (100), and (d) (2̅01) Facets of β-Ga2O3 on Amorphous SiO2.

β-Ga2O3 on amorphous SiO2 (001) (010) (100) (2̅01)
Ei (eV/Å2) 0.280 0.126 0.289 0.245
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A schematic of the solid-phase epitaxy process of β-Ga2O3 films as a function of temperature (from 600 to 1000 °C), shown in Figure 5, was thus developed, where the substrate temperature of the as-deposited film is 600 °C. Here, the Ga2O3 film is divided into the top (over 100 nm) and bottom (below 100 nm) regions, which show the inclusions of the structure. As the annealing temperature increases, the grain size of β-Ga2O3 and the nanofilm thickness of amorphous SiO2 also increase. The as-deposited β-Ga2O3 film structure shows the (100) preferred facet in the bottom region and the random orientation mixed with amorphous in the top region, which was confirmed by the diffused rings seen in the SAED pattern presented in Figure 3a. However, other peaks were present in the 200 nm as-deposited film, indicating that the bottom region of the film has the preferred (100) facet, whereas the top region has a polycrystalline structure, as shown in Figure 5a. Based on the presence of the sharper and higher quantity of dots in the SAED pattern (Figure 3b), the remnant amorphous structures will turn into the β-Ga2O3 crystalline phase when the annealing temperature is 800 °C, as shown in Figure 5b. Further increasing the annealing temperature to 1000 °C caused the appearance of TBs and SFs to release the internal strain, as shown in Figure 5c. TBs and SFs are harmful to electrical properties, as they reduce carrier mobility.39

Figure 5.

Figure 5

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Schematic of the solid-phase epitaxy process of the 200 nm Ga2O3 films as a function of annealing temperature: (a) as-deposited, (b) at 800 °C, and (c) at 1000 °C. The substrate temperature of the as-deposited film is 600 °C. The schematic is divided by a dotted line into the top (over 100 nm) and bottom (below 100 nm) regions, which show the inclusions of the structure.

For the photo/dark current contrast ratio (Iph/Idark), Figure S1a,b shows the annealing temperature-dependent current–voltage (I–V) characteristics of MSM PDs fabricated with 100 and 200 nm RTA-treated Ga2O3 films, respectively. Figure S2 shows the extracted spectral responsivity for the β-Ga2O3 PDs with 100 nm (a) and 200 nm (b) thin films using responsivity = (Iph – Idark)/(PA), where P is the power density of the incident light and A is the effective illuminated area.45Table 2 summarizes the optoelectronic properties of PDs with annealed β-Ga2O3 films. The responsivity and Iph/Idark ratio at 5 V bias increase with the annealing temperature increasing from 700 to 800 °C, corresponding to the grain growth and the reduced amorphous structure, while they decrease from 800 to 900 °C, as listed in Table 2, corresponding to the increasing TBs and SFs. The responsivity and Iph/Idark decrease due to electrons trapped in the defect trapping states, including the amorphous structure, TBs, SFs, and so on. These defects will capture the carriers generated by optical absorption, leading to the reduction of responsivity and Iph/Idark. From 900 to 1000 °C, Iph/Idark is almost equal to 1, which suffers from a high Idark value due to high-density TBs and SFs, similar to the effect of threading dislocations.46 The responsivity of the Ga2O3 film at an annealing temperature of 1000 °C exhibited the highest responsivity value in a broad range of light wavelengths, as shown in Figure S2a. Therefore, this film showed low discrimination (LD) for deep ultraviolet photodetector applications, as listed in Table 2.

Table 2. Tabulation of Ga2O3 with 100 and 200 nm Metal–Semiconductor–Metal Photodetectors in Various RTA Treatments from 700 to 1000 °Ca.

thermal treatment (°C) λpeak (nm) responsivity (A/W) at 5 V Iph/Idark at 5 V
RTA 700 (100 nm) 240 9.7 × 10–3 2.4 × 101
RTA 800 (100 nm) 230 7.95 × 10–2 3.49 × 102
RTA 900 (100 nm) 210 4.98 × 10–2 2.32 × 102
RTA 1000 (100 nm)   LD 1.17
RTA 700 (200 nm)   LD 3.44
RTA 800 (200 nm) 230 7.02 × 10–1 3.91 × 102
RTA 900 (200 nm) 240 4.85 × 10–2 3.96 × 101
RTA 1000 (200 nm)   LD 2.02
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a

LD, low discrimination.

For the optical characteristics of β-Ga2O3, since the silicon substrate is an opaque material in the ultraviolet–visible range, the substrate should be replaced with a transparent material such as glass or sapphire. Thus, the sapphire substrate was employed for optical measurement. The Eg of the Ga2O3 film was 4.95 eV for the as-deposited film. By increasing the annealing temperature from 700 to 1000 °C by RTA treatments, the Eg of Ga2O3 films increased from 4.95 to 5.00 eV. The maximum responsivity was blue-shifted, which was due to the wide band gap of Ga2O3 films, as summarized in Table 2. These results were published in our previous study.40

In a detailed comparison, the RTA at 700 °C (200 nm) has lower Iph/Idark and discrimination of responsivity than the RTA at 700 °C (100 nm) due to the high-ratio amorphous structure and grain boundaries (random orientation) on the top region, which is far from the substrate during sputtering (at 600 °C), resulting in high Idark. On the contrary, the thin film with RTA at 800 °C (200 nm) has revealed a much better photodetector performance than the thin film with RTA at 800 °C (100 nm) due to grain growth and the reduced amorphous structure. Obviously, the absorption region of 200 nm is dominated by the top region, where no coherent strain is induced for random orientation. Besides, the thicker the film, the larger the grain can grow, resulting in reduced grain boundaries, as listed in Table 2. In other words, the most stable interface (the greatest bonding energy calculated by DFT) formed by the (100) preferred orientation may hinder the coalescence of grains after annealing at 800 °C. This orientation is easy to form the twin structure or stacking faults, forming more planer defects and deteriorating the detecting performance, as shown in Figure 5 and listed in Table 2.

Consequently, the maximum responsivity was 0.702 and 7.95 × 10–2 A/W (λpeak = 230 nm) at 5 V bias with RTA treatment at 800 °C for 200 nm and 100 nm thin films, respectively. The maximum Iph/Idark values were 3.91 × 102 and 3.49 × 102 with RTA treatment at 800 °C for 200 and 100 nm thin films, respectively. Because 200 nm thick Ga2O3 films were formed by two times deposition, they took a longer deposition process than 100 nm thick Ga2O3 films at 600 °C. The film quality of 200 nm thick Ga2O3 films can be further improved because the substrate heater supports the thermal energy annealing the films for a long time, leading to more structural relaxation. Therefore, the thin film with RTA at 800 °C (200 nm) has revealed a much better photodetector performance than the thin film with RTA at 800 °C (100 nm) due to the better crystallinity of β-Ga2O3 in the former. The shortest rise time was 6.0 s and the falling time was 0.1 s for PDs with RTA treatment at 800 °C, as shown in Figure S3. These optoelectronic properties of PDs are in complete agreement with TEM, XRD, and schematic of the solid-phase epitaxy process results.

3. Conclusions

In summary, the results presented here demonstrate that the (100) facet of β-Ga2O3 for a layer thickness of 100 nm is the most preferred orientation on a (111) p-type silicon wafer with the native amorphous nano-oxide film on the surface. The interfacial bonding energy per unit area (Ei) between β-Ga2O3 films with various facets ((001), (010), (100), and (2̅01)) and amorphous SiO2 was calculated using density functional theory. The Ei of β-Ga2O3 (100)/SiO2 reveals the highest value (0.289 eV/Å2), which is consistent with the (100) preferred orientation of deposited films. In addition, just a few layers of SiO2 (about 10 Å) can affect the preferred orientation of β-Ga2O3.

The X-ray diffraction (XRD) results indicate both the as-deposited and postannealing films with the (400) preferred orientation for a layer thickness of 100 nm. However, slight random orientation with the amorphous structure is mixed in the preferred one for the as-deposited film with a thickness of 200 nm and reduced after being annealed at 800 °C, which is observed by XRD and transmission electron microscopy (TEM). Meanwhile, thermal-induced massive twin boundaries (TBs) and stacking faults (SFs) were generated when annealed at 1000 °C, owing to the relaxation of lattice strain by the coherent interface.

The responsivities, photo/dark current contrast ratio (Iph/Idark), and the discrimination of responsivity are inversely proportional to defect states, including the amorphous structure, grain boundaries, TBs, and SFs. For the 100 nm thin film, from 700 to 800 °C, the responsivity and Iph/Idark are proportional to better crystallinity in the RTA-treated β-Ga2O3 PDs. However, the stable interface formed by β-Ga2O3 (100) preferred orientation may hinder the coalescence of grains, limiting the improved performance. From 800 to 900 °C, the responsivity and Iph/Idark decrease due to electrons trapped in the defect trapping states, caused by planar defects such as TBs and SFs. From 900 to 1000 °C, Iph/Idark is almost equal to 1 and the low discrimination of responsivity due to higher-density TBs and SFs, which is similar to the effect of the threading dislocation.46 In contrast, the thin film with RTA at 800 °C (200 nm) has revealed a much better photodetector performance than the thin film with RTA at 800 °C (100 nm) since there is an additional layer with random orientation β-Ga2O3 on the former, where less coherent strain is induced. The maximum responsivity and Iph/Idark were 0.702 A/W (λpeak = 230 nm) and 3.91 × 102 at 5 V bias with RTA treatment at 800 °C for the 200 nm thin film, respectively. This study reveals the importance of interfacial characteristics that may play a key role in the photodetector properties of the deposited β-Ga2O3 on the Si substrate.

4. Materials and Methods

4.1. Materials, Preparation, and Annealing Conditions

Prior to deposition, p-type Si (p-Si) with (111) orientation was cleaned sequentially by submerging in acetone, isopropyl acetone, and deionized water for 30 min. Then, p-Si (111) substrates were further dipped into a hydrogen fluoride solution (49% concentrated) for 1 min to remove native SiO2. The base pressure of the vacuum chamber was lower than 2 × 10–6 torr. A working pressure of 5 × 10–3 torr was maintained using a gas mixture of Ar/O2 (10/2 sccm), and the applied RF power level was set as 100 W. During sputtering, the 100 nm thick and 200 nm thick Ga2O3 films were sputtered onto 2 inch p-Si (111) substrates at 600 °C using a 3 inch Ga2O3 ceramic target with 4 N purity. After growth, the as-deposited samples were annealed in an RTA chamber in an ambient air atmosphere for 1 min at various annealing temperatures (700, 800, 900, and 1000 °C).

4.2. Characterization and Photodetector Measurements

The composition depth profiling was conducted in an analyzed area by glow discharge optical emission spectroscopy (GDOES, GD-Profiler 2, Horiba Jobin Yvon). The crystallinity of the Ga2O3 films was then examined by XRD (PANalytical, X’Pert Pro MRD) and the corresponding microstructure was examined by TEM (JEOL JEM-2100F).

For the fabrication process of metal–semiconductor–metal (MSM) PDs, the Ti/Au (40/60 nm) Schottky contacts were deposited using an electron-beam evaporator, defined by conventional photolithography and lift-off techniques. The device area, finger width, and interspacing were 1.05 × 1.05 mm2, 50 and 50 μm, respectively, as shown in Figure S4. For device performance tests, the spectral responsivity measurements of Ga2O3 PDs were carried out under a bias voltage of 5 V using a spectrometer (Omni3029i) with a 30 W deuterium lamp light source (Zolix, LSH-D30) and a standard synchronous detection scheme measured at 60 Hz in this study.

4.3. Interfacial Bonding Energy of the Heterostructure per Unit Area (Ei) Calculations via Density Functional Theory (DFT) Simulations

DFT simulations were performed using the Vienna Ab initio Simulation Package47−49 to obtain the interfacial bonding energy of the heterostructure between the Ga2O3 films and the oxide of the Si substrate. The atomic geometries of β-Ga2O3 with (001), (010), (100), and (2̅01) facets on amorphous SiO2 are shown in Figure 6a–d, respectively. The electron–ion interactions of each atom were expressed by the projector augmented wave method.50 The Perdew–Burke–Ernzerhof function with a generalized gradient approximation was used to deal with the electron exchange and correlation.51 An energy cutoff of 500 eV with a force threshold of 0.0001 eV/A was used for the wave function expansion. A supercell of approximately 850 atoms was assumed to have a vacuum thickness of 20 Å to ensure the decoupling of consecutive slabs. The 1 × 1 × 1 mesh of a γ-centered Monkhorst–Pack52k-point grid was used for the geometric optimization of static energy and to optimize the electronic structure. To emulate SiO2 on a substrate, three bottom SiO2 layers were fixed and leftover atomic position layers were fully relaxed. The interfacial bonding energy of the heterostructure between various facets of the β-Ga2O3 films ((001), (010), (100), and (2̅01)) and the amorphous SiO2 per unit area (Ei) was calculated as follows

4.3. 1

where Ei is the heterostructure’s interfacial bonding energy per unit area, A is the area of the β-Ga2O3/SiO2 heterostructure, Evac/Ga2O3/SiO2 is the total energy of vacuum/β-Ga2O3/SiO2, Evac/Ga2O3/Vac is the total energy of the vacuum/β-Ga2O3/vacuum slab, and Evac/SiO2 is the total energy of the vacuum/SiO2 slab. All simulated atomic configuration results were visualized using open-source OVITO.53

Figure 6.

Figure 6

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Perspective views of the atomic geometry of β-Ga2O3 with (a) (001), (b) (010), (c) (100), and (d) (2̅01) facets on amorphous SiO2 for the interfacial bonding energy per unit area (Ei) based on density functional theory (DFT) calculations. The cream, bronze, and red atoms represent silicon, gallium, and oxygen, respectively.

Acknowledgments

This work was financially supported by the Ministry of Science and Technology of Taiwan under Grant Nos. MOST 108-2221-E-005-028-MY3, 108-2221-E-005-072-MY3, 109-2221-E-009-058, 110-2811-E-005-023-MY3, and 110-2221-E-005-510-MY3. The work was also supported by the “Innovation and Development Center of Sustainable Agriculture” from the Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan, as well as the National Center for High-performance Computing (NCHC) of National Applied Research Laboratories (NARLabs) in Taiwan for providing computational and storage resources.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.1c04380.

  • Electronic and optical characterization and experimental process details, including I–V characteristics; spectral response; normalized current with the rise time and falling time; and schematic diagram of metal–semiconductor–metal for photodetectors (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao1c04380_si_001.pdf (293.2KB, pdf)

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