Search

β-Ga2O3, an emerging wide bandgap semiconductor material, holds significant potential for various applications. However, challenges persist in improving the crystal quality and achieving controllable doping of β-Ga2O3. In particular, the relationship between these factors and the mechanisms behind them are not fully understood. Molecular beam epitaxy (MBE) is viewed as one of the most sophisticated techniques for growing high-quality crystalline films. It also provides a platform for studying the effects of doping and defects in heteroepitaxial β-Ga2O3. In our study, we tackled the issue of Si source passivation during the MBE growth of Si-doped β-Ga2O3. We did this by using an electron beam vaporize module, a departure from the traditional Si effusion cell. Our research extensively explores the correlation between Si doping concentration and film properties. These properties include microstructure, morphology, defects, carrier conductivity, and mobility. The results from these investigations are mutually supportive and indicate that a high density of defects in heteroepitaxial β-Ga2O3 is the primary reason for the challenges in controllable doping and conductivity. These insights are valuable for the ongoing development and enhancement of β-Ga2O3-based device techniques. [ABSTRACT FROM AUTHOR]

The effect of high temperature annealing under O2 and N2 atmospheres on the electrical properties and defect formation on Sn doped n-type β-Ga2O3 bulk samples was investigated by electron paramagnetic resonance (EPR) spectroscopy. EPR, being a volume sensitive technique, probes the entire sample volume. Our results show an electrical compensation being correlated with the formation of a negatively charged Ga vacancy defect VGa2−. This VGa center is different from the one observed after particle irradiation. The associated shift of the Fermi level reveals the presence of Fe3+, Cu2+, and Cr3+, which are residuals related to the growth conditions. The 1100 °C N2 annealed sample is fully compensated, and the neutral donor resonance is no longer observed. Our results directly confirm the thermal instability of Ga and Sn in n-type conducting samples. No oxygen vacancy related centers were detected. We discuss the various Ga vacancy centers reported previously. [ABSTRACT FROM AUTHOR]

High performance β–Ga2O3 trench Schottky barrier diodes (SBDs) were demonstrated with the employment of a novel etching technique called self-reactive etching (SRE). Owing to the high-quality surface without any etched damages and impurities, the β–Ga2O3 trench SBDs showed temperature-dependent electrical characteristics. Negligible charge trapping and hysteresis indicated the high quality of the interface between the Al2O3 dielectric and the β–Ga2O3 layer. Only a few changes of the capacitance–voltage curves measured at different temperatures have been shown, suggesting an excellent thermal stability. A high current density of 1228 A cm−2 and ION/IOFF ratio of 1010 indicated the excellent rectifying characteristics. An ideality factor of 1.23 and barrier height of 1.58 eV confirmed the surface repair and reconstruction from the SRE process. These results indicate that SRE can be beneficial for the β–Ga2O3 etching and the future development of β–Ga2O3 power electronics. [ABSTRACT FROM AUTHOR]

We designed an original and effective method to study the laser damage mechanism of a β-Ga2O3 single crystal grown by the edge-defined film-fed growth (EFG) method. Structure destruction under irradiation with a high light field intensity of 1064 nm using an Nd:YAG laser was systematically studied in the β-Ga2O3 crystal. Four typical crystal defects, namely, voids, amorphous and nanocrystalline layers and high density stacking faults, were found using a focused ion beam–dual beam scanning electron microscope (FIB-SEM) and a transmission electron microscope (TEM). For the first time, a laser damage mechanism in the β-Ga2O3 subsurface layer was built up and illuminated by microstructure analysis. The stacking fault relaxation of the β-Ga2O3 single crystal was observed in situ for the first time under electron beam irradiation. The cathodoluminescence (CL) spectrum further revealed the luminescence properties of the stacking faults. [ABSTRACT FROM AUTHOR]

Herein, bandgap tuning of monoclinic (−201)‐oriented β‐(AlxGa1−x)2O3 thin films is achieved through a β‐Ga2O3/Al2O3 heterojunction by a feasible annealing process with an O2 atmosphere. During the annealing process, Al atoms of the Al2O3 substrate outdiffuse easily into the β‐Ga2O3 thin film deposited by ozone‐assisted molecular beam epitaxy (OMBE). The Al compositions in the β‐(AlxGa1−x)2O3 samples are tuned through adjusting the annealing temperature from 800 to 1300 °C and experimentally determined from the result of X‐ray photoelectron spectroscopy (XPS) measurements combined with Vegard's law. Successive Al‐composition‐gradient β‐(AlxGa1−x)2O3 thin films with controlled bandgap are constructed. On these bases, β‐Ga2O3 thin films are deposited on β‐(AlxGa1−x)2O3 (0 ≤ x ≤ 0.65) substrates through OMBE, yielding β‐Ga2O3/β‐(AlxGa1−x)2O3 (0 ≤ x ≤ 0.65) heterojunction structures, and the band offsets of this heterojunction are determined by XPS accordingly. This methodology to achieve high‐quality β‐(AlxGa1−x)2O3 thin films with adjustable Al composition and tunable band offsets of the β‐Ga2O3/β‐(AlxGa1−x)2O3 interface will provide guidance for potential strategies to develop and fabricate β‐(AlxGa1−x)2O3‐based deep‐UV photodetectors and power devices. [ABSTRACT FROM AUTHOR]

In this Letter, self-reaction etching (SRE) with Ga flux demonstrates the capability of eliminating surface contaminations and damage, as well as improving the electrical characteristics of the interface between monoclinic gallium oxide (β-Ga2O3) and the insulator. Compared to post-tetramethyl ammonium hydroxide wet chemical treatment, SRE is a low damage repair method that effectively removes surface contaminants introduced during previous inductively coupled plasma etching of β-Ga2O3 without surface damage. As a consequence, the surface band bending on the β-Ga2O3 surface decreased as demonstrated by the core-level peak shifts of x-ray photoemission spectroscopy, which indicated fewer negative charges remained on the surface. Furthermore, the interface state density (Dit) between β-Ga2O3 and an Al2O3 insulator was determined by using high-temperature conductance and photoassisted C–V measurements. The Dit dropped significantly for samples treated by SRE as compared with other treatments. These results suggested that SRE is an attractive etching candidate for future Ga2O3 power device fabrication. [ABSTRACT FROM AUTHOR]

A low‐resistance Ohmic contact of Pd/Pt/Au metallization scheme is formed on a p‐type GaN film grown by metal‐organic chemical vapor deposition (MOCVD). Two samples are prepared to explore the effect of contaminations at the metal and GaN interface on the properties of the Ohmic contact. One directly transfers the fresh GaN film from MOCVD to the metal deposition chamber through an ultrahigh vacuum (UHV) tube, without exposing the GaN surface to air; the other transfers the GaN film from MOCVD to metal deposition through the atmosphere. The results show a lower specific contact resistance (6.2 ± 0.9) × 10−5 Ω cm2 for the directly UHV‐transferred sample than the air‐transferred sample (2.1 ± 0.9) × 10−4 Ω cm2. Once exposed to air, carbonaceous particles and an amorphous oxide layer easily adhere to the p‐type GaN surface, which not only increase the Schottky barrier height but also generate more grain boundaries in the Pd/Pt/Au stacks. The grain boundaries, acting as diffusion channels, make Au atoms diffuse easily into the Pd layer and propagate to the p‐GaN surface layer after annealing. Therefore, the Ohmic contact fabricated in UHV ambience with lower oxygen and carbon contaminations at the interface shows superior characteristics than the samples prepared by the traditional method. [ABSTRACT FROM AUTHOR]

Growth mechanism and temperature of monoclinic gallium oxide (β‐Ga2O3) films grown by ozone molecular beam epitaxy (MBE) are investigated herein. Phase‐pure (2¯01) β‐Ga2O3 films can be grown on c‐plane sapphire substrates when the growth temperature exceeds 500 °C, and the grain size increases with the increase in the growth temperature. Sixfold rotational domains are obtained based on the epitaxial relationships (Ga2O3 < 010>//Al2O3<11¯00> and Ga2O3 < 102>//Al2O3 < 112¯0>). For the film grown at 700 °C, the threefold facets are observed for the first time, which are resulted from the easy‐cleaved (100) plane and rotational domains. In addition, the cathodoluminescence spectra of the β‐Ga2O3 films show that the proportion of ultraviolet emission increases with the increase in the growth temperature, which is attributed to the modulation of defect. Finally, the growth rate can be modulated by the ratio of Ga flux and ozone pressure. A reference is provided for heteroepitaxy of β‐Ga2O3 films and better understanding of the ozone MBE growth mechanism of oxides. [ABSTRACT FROM AUTHOR]

The realization of electrically pumped lasers at deep sub-micro and nanometer scale operating far beyond the diffraction limit is still a crucial goal in nanophotonics and plasmonics for prospective fundamental research and application. Herein, electrically pumped spasing action was captured from a cross-stacked architecture composed of a single Ga-doped ZnO microwire (ZnO:Ga MW) crossed with another ZnO:Ga MW covered by Au nanoparticles. To exploit the spasing feature, a plasmonic nanocavity could be constructed based on the sandwiched structures, with isolated Au nanoparticles filling the spacer between the crossed MWs. When both emission regions from the crossed MWs overlapped with each other, the cross-stacked architecture exhibited quasi-Schottky junction behavior, resulting in the formation of a tunneling junction. When the injection current exceeded certain values, bright and localizing emissions were observed at the crossed regions, with a sharp peak emerging in the emission spectra. The dominant emission wavelengths centered at 550 nm were accompanied by the spectral linewidth rapidly narrowing to 2 nm, suggesting a transition from spontaneous to stimulated emission. The electrically pumped lasing characteristics can be attributed to efficient metal plasmons amplification by the stimulated emission of radiation from Au nanoparticles, which filled the nanocavities. Therefore, this cross-stacked architecture provides a natural route towards electrical injection schemes that can be employed to construct electrical-pumping spasers. This technology also provides a candidate to investigate the fabrication of tunneling diodes. [ABSTRACT FROM AUTHOR]

Individual Sb-doped ZnO (ZnO:Sb) microwires with durable and reproducible p-type conduction have been synthesized, and by increasing the Sb2O3 weight ratios in the precursor mixtures, tunable p-type conduction characteristics can be obtained. Meanwhile, wavelength-tuning electroluminescence (EL) has been observed by applying bias onto individual ZnO:Sb microwires, in which the ZnO:Sb microwires act as emitting filaments. The as-synthesized p-type ZnO:Sb microwires are applied to fabricate homojunction light-emitting devices. The corresponding p–n junction demonstrates excellent diode characteristics, and strong near band edge emissions can be observed with the dominant EL emission wavelengths centered at 400 nm. The results demonstrated the emitting filament characteristics of ZnO:Sb microwires for the first time, and also demonstrated their applicability in homojunction light-emitting diodes, and thus may offer alluring prospects as compact, efficient, reliable building blocks for microscale light sources. [ABSTRACT FROM AUTHOR]

• Atomic arrangement of (101) surface was terminated either by Ga or O. • Dangling bond density on (101) surface was 2–3 times higher than (010) surface. • Surface and Schottky barrier height of (101) plane were 1.14 eV and 1.07 eV. • Fast etching rate of (101) plane was observed for wet chemical etch. • The potential applications of (101) plane were also evaluated. [Display omitted] This work studied the structural, thermal, optical and electrical properties of β -Ga 2 O 3 (101) plane with high-density surface dangling bonds for the first time. The high quality (101)-oriented substrate with a full width at half maximum (FWHM) of 90″ in X-ray rocking curve was grown by the edge-defined film-fed growth (EFG) method. The atomic arrangement of (101) surface was terminated either by Ga or O. The dangling bond densities of Ga- and O-terminated surfaces were calculated to be 2.230 × 1015 cm−2 and 2.376 × 1015 cm−2, respectively. The thermal property of the (101) plane was characterized. The Raman active modes of the (101) plane were allowed for selective observation with the variation of polarizing angle. The surface and Schottky barrier height of the (101) plane were estimated to be as low as 1.14 eV and 1.07 eV by optical and electrical measurements, respectively. The activation energy for wet chemical etching was determined to be 0.451 eV for (101) plane and the high etching rate was obtained. By comprehensive comparisons with other common planes, the potential applications of β -Ga 2 O 3 (101) plane should be comparable to the widely used 2 ̅ 01 plane. [ABSTRACT FROM AUTHOR]

• The optical bandgap anisotropy of β -Ga 2 O 3 in deep ultraviolet band was studied. • The surface barrier heights of a , b , c planes were 1.30, 1.25 and 1.30 eV. • The angle-resolved ultraviolet transmittance spectra of a , b , c planes were obtained. • The high polarization filtering performance of β -Ga 2 O 3 was demonstrated. As a deep ultraviolet transparent conducting semiconductor, β -Ga 2 O 3 has been actively studied for short wavelength optical and optoelectronic applications. This study investigated the anisotropy of optical properties, valence band structures, and the in-plane angle-resolved transmittance spectra of the three main crystal planes. The optical bandgaps of unintentionally doped β -Ga 2 O 3 (100), (010), and (001) planes were 4.70, 4.55, and 4.70 eV, respectively. The valence band maximum of the (100), (010), and (001) planes obtained by VB-XPS were 3.4, 3.3, and 3.4 eV, respectively. A 0.05 eV larger surface bending band was found in the (100) and (001) planes than in the (010) plane. The transmitted intensity was established as a function of the in-plane polarization angles. The polarized optical bandgaps of E// a , E// b , and E// c were fit to 4.58, 4.73, and 4.48 eV, respectively, indicating that β -Ga 2 O 3 can be used in polarization filtering and spectrally selective photodetectors in the UVC band, which was also demonstrated using two vertically stacked (100) single crystal wafers. [ABSTRACT FROM AUTHOR]

The UV-vis photodetector (PD), a detector that can simultaneously detect light in the ultraviolet region and the visible region, has a wide range of applications in military and civilian fields. Currently, it is very difficult to obtain good detection performance in the UV region (especially in the solar-blind range) like in the visible region with most UV-vis PDs. This severely affects the practical application of UV-vis broad-spectra PDs. Here, a simple sandwich structure PD (SSPD) composed of β-Ga 2 O 3 , Au electrodes, and the MAPbBr 3 perovskite is designed and fabricated to simultaneous enhance the detection performance in the UV and visible light regions. The β-Ga 2 O 3 /Au/MAPbBr 3 SSPD exhibits enhanced optoelectronic performance with high responsivities of 0.47 and 1.43 A W -1 at 240 and 520 nm under a bias of 6 voltage (V), respectively, which are 8.5 and 23 times than that of the metal-semiconductor-metal (MSM) structure MAPbBr 3 PD at 6 V, respectively. The enhanced performance was attributed to the effective suppression of carrier recombination due to the efficient interface charge separation in the device structure. In addition, the self-powered response characteristic is also realized by forming a type-II heterojunction between β-Ga 2 O 3 and MAPbBr 3 , which gives the β-Ga 2 O 3 /Au/MAPbBr 3 SSPD superior single-pixel photo-imaging ability without an external power supply. This work provides a simple and effective method for the preparation of high-performance self-powered imaging PDs in the UV-visible region.

As a kind of photodetector, position-sensitive-detectors (PSDs) have been widely used in noncontact photoelectric positioning and measurement. However, fabrications and applications of solar-blind PSDs remain yet to be harnessed. Herein, we demonstrate a solar-blind PSD developed from a graphene/Ga 2 O 3 Schottky junction with a 25-nanometer-thick Ga 2 O 3 film, in which the absorption of the nanometer-thick Ga 2 O 3 is enhanced by multibeam interference. The graphene/Ga 2 O 3 junction exhibits a responsivity of 48.5 mA/W and a rise/decay time of 0.8/99.8 μs at zero bias. Moreover, the position of the solar-blind spot can be determined by the output signals of the PSD. Using the device as a sensor of noncontact test systems, we demonstrate its application in measurement of angular, displacement, and light trajectory. In addition, the position-sensitive outputs have been used to demodulate optical signals into electrical signals. The results may prospect the application of solar-blind PSDs in measurement, tracking, communication, and so on.

The usage of ZnO as active layers to fabricate hybrid heterojunction light-emitting diodes is expected to be an effective approach for ultraviolet light sources. Individual ZnO microwires with controlled gallium (Ga) incorporation (ZnO/Ga MWs) have been fabricated via a chemical vapor deposition method. It is found that with the increasing Ga-incorporated concentration, the near-band-edge (NBE) photoluminescence of the ZnO MWs blue-shifted gradually from 390 to 370 nm. Heterojunction diodes comprising single ZnO/Ga MWs and p-GaN have been fabricated. With increasing injection currents, the interfacial emissions can be suppressed effectively and the typical NBE emission dominates the electroluminescence (EL). In particular, with increasing Ga-doping concentration, the dominant EL emission wavelengths of the ZnO/Ga MW-based heterojunction diodes blue-shifted from 384 to 372 nm, and the blue shift can be ascribed to the Burstein-Moss effect induced by the Ga incorporation. The present work demonstrates the feasibility of optical band gap engineering of ZnO MWs and the potential application for wavelength-tuning ultraviolet light sources.