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In this work, a systematic photoluminescence (PL) study on three series of gallium oxide/aluminum gallium oxide films and bulk single crystals is performed including comparing doping, epitaxial substrates, and aluminum concentration. It is observed that blue/green emission intensity strongly correlates with extended structural defects rather than the point defects frequently assumed. Bulk crystals or Si-doped films homoepitaxially grown on (010) β-Ga2O3 yield an intense dominant UV emission, while samples with extended structural defects, such as gallium oxide films grown on either (-201) β-Ga2O3 or sapphire, as well as thick aluminum gallium oxide films grown on either (010) β-Ga2O3 or sapphire, all show a very broad PL spectrum with intense dominant blue/green emission. PL differences between samples and the possible causes of these differences are analyzed. This work expands previous reports that have so far attributed blue and green emissions to point defects and shows that in the case of thin films, extended defects might have a prominent role in emission properties.

Diffusion of native defects such as vacancies and their interactions with impurities are fundamental to semiconductor crystal growth, device processing, and design. However, the transient equilibration of native defects is difficult to directly measure. We used (AlxGa1−x)2O3/Ga2O3 superlattices (SLs) to detect and analyze transient diffusion of cation vacancies during annealing in O2 at 1000–1100 °C. Using a novel finite difference scheme for diffusion with time- and space-varying diffusion constants, we determined diffusion constants for Al, Fe, and cation vacancies, including the vacancy concentration dependence for Al. In the case of SLs grown on Sn-doped β-Ga2O3 (010) substrates, gradients observed in the extent of Al diffusion indicate a supersaturation of vacancies in the substrates that transiently diffuse through the SLs coupled strongly to Sn and thus slowed compared to undoped cases. In the case of SLs grown on (010) Fe-doped substrates, the Al diffusion is uniform through the SLs, indicating a depth-uniform concentration of vacancies. We find no evidence for the introduction of VGa from the free surface at rates sufficient to affect Al diffusion at at. % concentrations, establishing an upper bound on surface injection. In addition, we show that unintentional impurities in Sn-doped Ga2O3 such as Fe, Ni, Mn, Cu, and Li also diffuse toward the surface and accumulate. Many of these likely have fast interstitial diffusion modes capable of destabilizing devices, thus suggesting that impurities may require further reduction. This work provides a method to measure transients in diffusion-mediating native defects otherwise hidden in common processes such as ion implantation, etching, and film growth. [ABSTRACT FROM AUTHOR]

We demonstrate a new substrate cleaning and buffer growth scheme in β-Ga2O3 epitaxial thin films using metal–organic vapor phase epitaxy (MOVPE). For the channel structure, a low-temperature (LT, 600 °C) un-doped Ga2O3 buffer was grown, followed by a transition layer to a high-temperature (HT, 810 °C) Si-doped Ga2O3 channel layers without growth interruption. The (010) Ga2O3 Fe-doped substrate cleaning uses solvent cleaning, followed by additional hydrofluoric acid (49% in water) treatment for 30 min before the epilayer growth. This step is shown to compensate the parasitic Si channel at the epilayer–substrate interface that originates from the substrate polishing process or contamination from the ambient. From secondary ion mass spectroscopy (SIMS) analysis, the Si peak atomic density at the substrate interface is found to be several times lower than the Fe atomic density in the substrate—indicating full compensation. The elimination of the parasitic electron channel at the epi–substrate interface was also verified by electrical (capacitance–voltage profiling) measurements. In the LT-grown (600 °C) buffer layers, it is seen that the Fe forward decay tail from the substrate is very sharp, with a decay rate of ∼9 nm/dec. X-ray off-axis rocking curve ω-scans show very narrow full width at half maximum (FWHM) values, similar to the as-received substrates. These channels show record high electron mobility in the range of 196–85 cm2/V⋅s in unintentionally doped and Si-doped films in the doping range of 2 × 1016–1 × 1020 cm−3. Si delta-doped channels were also grown utilizing this substrate cleaning and the hybrid LT buffers. Record high electron Hall mobility of 110 cm2/V⋅s was measured for sheet charge density of 9.2 × 1012 cm−2. This substrate cleaning, combined with the LT buffer scheme, shows the potential of designing Si-doped β-Ga2O3 channels with exceptional transport properties for high-performance Ga2O3-based electron devices. [ABSTRACT FROM AUTHOR]

We report a new type of structural defect in β-Ga2O3 homoepitaxial thin films grown by metalorganic vapor phase epitaxy, which we have dubbed as "sympetalous defects." These consist of a line defect (for example, a nanotube defect) in the underlying substrate combined with a multi-faceted inverted polycrystalline pyramid in the epitaxial film, which may also be decorated with twinned polycrystalline grains. In plan-view atomic force, scanning electron, or optical microscopies, the sympetalous defects appear similar in shape to polygonal etch pits observed for single crystals. Photoluminescence microscopy exposed spots of polarization-dependent luminescence at these defects, different from the single crystal films' luminescence. Furthermore, some of the defects exhibited circular dichroism in their luminescence that we correlated with partial helices formed within the pits by the arrangement of linearly dichroic polycrystalline grains. Finally, the density of sympetalous defects agrees with the etch pit densities of the substrates. Understanding and controlling these defects will be of importance as they modify the local properties of films, affect fabricated device yields, and influence characterization experiments. [ABSTRACT FROM AUTHOR]

In this letter, fin-shape tri-gate $\beta $ -Ga2O3 lateral MESFETs are demonstrated with a high power figure of merit (PFOM) of 0.95 GW/cm2 – a record high for any $\beta $ -Ga2O3 transistor to date. A low-temperature un-doped buffer-channel stack design is developed which demonstrates record high Hall and drift electron mobilities in doped $\beta $ -Ga2O3 channels allowing for low ON resistances (RON) in $\beta $ -Ga2O3 MESFETs. Fin-widths (Wfin) were 1.2- $1.5~\mu \text{m}$ and there were 25 fins (Nfin) per device with a trench depth of $\sim ~1~\mu \text{m}$. A $\beta $ -Ga2O3 MESFET with a source-drain length of 6.4 $\mu \text{m}$ exhibits a high ON current (187 mA/mm), low RON ($20.5~\Omega $.mm) and a high average breakdown field (4.2 MV/cm). All devices show very low reverse leakage until catastrophic breakdown for breakdown voltages (VBR) scaling from 1.1kV to ~3kV. This work demonstrates the potential of channel engineering in improving $\beta $ -Ga2O3 device performance towards lower conduction losses for low-to-medium voltage applications. [ABSTRACT FROM AUTHOR]

β -Ga2O3 metalâ€"semiconductor field-effect transistors are realized with superior reverse breakdown voltages (V BR) and ON currents (I DMAX). A sandwiched SiN x dielectric field plate design is utilized that prevents etching-related damage in the active region and a deep mesa-etching was used to reduce reverse leakage. The device with L GD = 34.5 ÎĽ m exhibits an I DMAX of 56 mA mmâˆ'1, a high I ON/ I OFF ratio >108 and a very low reverse leakage until catastrophic breakdown at ∼4.4 kV. A power figure of merit (PFOM) of 132 MW cmâˆ'2 was calculated for a V BR of ∼4.4 kV. The reported results are the first >4 kV class Ga2O3 transistors to surpass the theoretical unipolar FOM of silicon. [ABSTRACT FROM AUTHOR]

High quality dielectric‐semiconductor interfaces are critical for reliable high‐performance transistors. This paper reports the in situ metal–organic chemical vapor deposition of Al2O3 on β‐Ga2O3 as a potentially better alternative to the most commonly used atomic layer deposition (ALD). The growth of Al2O3 is performed in the same reactor as Ga2O3 using trimethylaluminum and O2 as precursors without breaking the vacuum at a growth temperature of 600 °C. The fast and slow near interface traps at the Al2O3/β‐Ga2O3 interface are identified and quantified using stressed capacitance–voltage (CV) measurements on metal oxide semiconductor capacitor (MOSCAP) structures. The density of shallow and deep level initially filled traps (Dit) are measured using ultraviolet‐assisted CV technique. The average Dit for the MOSCAP is determined to be 6.4 × 1011 cm−2eV−1. The conduction band offset of the Al2O3/ Ga2O3 interface is also determined from CV measurements and found out to be 1.7 eV which is in close agreement with the existing literature reports of ALD Al2O3/Ga2O3 interface. The current–voltage characteristics are also analyzed and the average breakdown field is extracted to be approximately 5.8 MV cm−1. This in situ Al2O3 dielectric on β‐Ga2O3 with improved dielectric properties can enable Ga2O3‐based high‐performance devices. [ABSTRACT FROM AUTHOR]

Monoclinic β-Ga 2 O 3 , an ultra-wide bandgap semiconductor, has seen enormous activity in recent years. However, the fundamental study of the plasmon-phonon coupling that dictates electron transport properties has not been possible due to the difficulty in achieving higher carrier density (without introducing chemical disorder). Here, we report a highly reversible, electrostatic doping of β-Ga 2 O 3 films with tunable carrier densities using ion-gel-gated electric double-layer transistor configuration. Combining temperature-dependent Hall effect measurements, transport modeling, and comprehensive mobility calculations using ab initio based electron-phonon scattering rates, we demonstrate an increase in the room-temperature mobility to 201 cm 2 V -1 s -1 followed by a surprising decrease with an increasing carrier density due to the plasmon-phonon coupling. The modeling and experimental data further reveal an important "antiscreening" (of electron-phonon interaction) effect arising from dynamic screening from the hybrid plasmon-phonon modes. Our calculations show that a significantly higher room-temperature mobility of 300 cm 2 V -1 s -1 is possible if high electron densities (>10 20 cm -3 ) with plasmon energies surpassing the highest energy LO mode can be realized. As Ga 2 O 3 and other polar semiconductors play an important role in several device applications, the fundamental understanding of the plasmon-phonon coupling can lead to the enhancement of mobility by harnessing the dynamic screening of the electron-phonon interactions.