The development of next-generation communication networks aims to provide faster and more reliable solutions in a small form factor. Visible light communication (VLC) has emerged as a promising complementary technology to traditional radio frequency wireless communication due to its exceptional efficiency, high modulation speeds, and freedom from the congested radio spectrum. Recent advancements have focused on gallium nitride (GaN)-based micro-light-emitting diodes (microLEDs) for VLC. However, these microLEDs typically require high injection current densities and high-frequency operation, necessitating the use of independent drivers and resulting in bulky systems. This study presents an innovative approach to overcome these limitations by heterogeneously integrating of 20x10 mu m2 blue microLEDs using transfer printing onto a GaN-based high electron mobility transistor (HEMT) target wafer grown on silicon carbide (SiC) substrate. This integration allows for a compact, single-chip platform where the emission from a single microLED is modulated by tuning the gate voltage of its GaN HEMT. The resulting on-chip system achieves with a modulation bandwidth of 100 MHz, maintaining a small form factor. Our findings suggest that this approach holds significant promise for the development of future large-scale VLC systems on a single chip, offering broad application prospects.

Compensating deep level defect states that influence the electrical properties of beta-phase gallium oxide (beta-Ga2O3) can be introduced intentionally through doping, or unintentionally through unwanted impurities and intrinsic defects. Understanding the complex behavior of these compensating centers is essential for optimizing beta-Ga2O3 for both high voltage and RF electronics. Applications in harsh environments, such as in space, add further complications due to defect creation resulting from high energy irradiation. Due to its inherent n-type conductivity, compensating deep acceptor states intentionally introduced by doping with Nitrogen, Iron or Magnesium to create semi-insulating regions of device structures are of great interest. However, inadvertent impurities such as Carbon are also predicted to create deep acceptors and can be problematic. The presence of intrinsic defects that form during growth or introduced by harsh environments makes the understanding of how defects impact material and device properties very complex. Here we use deep level transient (thermal) spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) to identify, compare and characterize individual deep acceptor states created by both extrinsic and intrinsic sources in beta-Ga2O3 and compare with theoretical predictions. Compensation efficiencies between acceptor choices are compared, and some of the more unusual behaviors of very deep states present below midgap are described, where both conduction and valence band transitions are observed and explained. Radiation studies used to differentiate extrinsic from intrinsic sources will be discussed in the context of unraveling the comprehensive impacts of defects in beta-Ga2O3.

GaAsSb/Si heterostructure photodiode was fabricated via transfer printing based on sacrificial layer wet etching. Then the dark I-V and photo I-V of GaAsSb on InP substrate and on Si substrate were compared to examine photodetection ability of the GaAsSb/Si diode. Finally, Capacitancefrequency (C-f) and Capacitance-Voltage (C-V) measurements were applied to investigate the influence of the printed interface on charge transport.

The impact of 3 MeV proton irradiation on Zinc- and Carbon doped AlGaInP was compared. Full bandgap characterization via DLTS and DLOS revealed several trap states at EV + 0.7 eV, EV + 1.0 eV, EV + 1.9 eV with an additional trap state observed after irradiation at EV + 0.4 eV. The EV + 1.9 eV state was found to be dominant in both trap concentration and trap introduction rate. The carrier removal rate was characterized and found to match the trap introduction for Zn- but not C-doping. Comprehensive defect characterization as a result of radiation damage is useful for informing the future design of radiation tolerant device design.

To date, the greatest performance limiter in monolithic III-V/Si tandem (multijunction) solar cells, like GaAs 0.75 P 0.25 /Si, is excess threading dislocation densities (TDD) resulting from the lattice-mismatched heteroepitaxy. Recent developments in low-TDD GaAs (y) P (1-) (y) /Si metamorphic buffers were used to grow standalone GaAs 0.75 P 0.25 top cells on Si with a TDD of 4 x 10 (6) cm (-2) , similar to 2.5 x lower than previous iterations, greatly improving the potential for the production of high-efficiency tandems based on this platform. Nonetheless, these reduced-TDD cells were still found to possess considerable voltage-dependent carrier collection (VDC) losses. As such, to improve J (SC) and fill factor, without sacrificial reduction in V (OC) , a doping gradient within the cell base layer was designed and implemented. The updated design reduces VDC losses to levels that would otherwise require further TDD reduction by at least another 2.5 x (to <= 1.5 x 10 (6) cm (-2) ) in a typical flat doping profile design. Replacing the p (+) -Ga 0.64 In 0.36 P back surface field with p (+) -Al 0.2 Ga 0.8 As 0.74 P 0.26 provided an additional improvement in both V (OC) and J (SC) , yielding device performance equivalent to a 4 x TDD reduction in the previous design. The culmination of these design changes results in a new subcell that outperforms our previous best top cell by similar to 4.3% absolute AM1.5G efficiency, with increases in fill factor, J (SC) , and W (OC) of about 3.3% absolute, 1.9 mA/cm (2) , and 0.12 V, respectively. This new design, coupled with the reduced TDD platform, paves a promising path toward the development of higher efficiency GaAs 0.75 P 0.25 /Si tandems upon full device integration.

This study provides a comprehensive analysis of the dominant deep acceptor level in nitrogen-doped beta-phase gallium oxide (β-Ga2O3), elucidating and reconciling the hole emission features observed in deep-level optical spectroscopy (DLOS). The unique behavior of this defect, coupled with its small optical cross section, complicates trap concentration analysis using DLOS, which is essential for defect characterization in β-Ga2O3. A complex feature arises in DLOS results due to simultaneous electron emission to the conduction band and hole emission to the valence band from the same defect state, indicating the formation of two distinct atomic configurations and suggesting metastable defect characteristics. This study discusses the implications of this behavior on DLOS analysis and employs advanced spectroscopy techniques such as double-beam DLOS and optical isothermal measurements to address these complications. The double-beam DLOS method reveals a distinct hole emission process at EV+1.3 eV previously obscured in conventional DLOS. Optical isothermal measurements further characterize this energy level, appearing only in N-doped β-Ga2O3. This enables an estimate of the β-Ga2O3 hole effective mass by analyzing temperature-dependent carrier emission rates. This work highlights the impact of partial trap-filling behavior on DLOS analysis and identifies the presence of hole trapping and emission in β-Ga2O3. Although N-doping is ideal for creating semi-insulating material through the efficient compensation of free electrons, this study also reveals a significant hole emission and migration process within the weak electric fields of the Schottky diode depletion region.

Si nanomembranes (NMs) with a thickness of 205 nm were grafted onto GaAsSb/InAlAs layers grown on InP via polydimethylsiloxane (PDMS)-stamp-assisted printing. The Si/GaAsSb heterostructure diodes exhibit promising electrical characteristics, paving the path for GaAsSb-Si integrated photodetectors.

A detailed study comparing defect incorporation between laser-assisted metal-organic chemical vapor deposition (MOCVD)-grown GaN and conventional low- and high-growth-rate MOCVD GaN was conducted. Using deep-level transient and optical spectroscopy, traps throughout the bandgap were characterized where traps were found at EC-0.25 eV, EC-0.57 eV, EC-0.72 eV, EC-0.9 eV, EC-1.35 eV, EC-2.6 eV, and EC-3.28 eV in all three samples. This indicates no new traps were observed in the laser-assisted MOCVD GaN sample. Overall, the trap concentrations in the laser-assisted MOCVD sample were ∼2× higher than the optimal low-growth-rate sample, but this is primarily due to the increase in gallium vacancy EC-2.6 eV and carbon-related EC-3.28 eV trap concentrations. The EC-0.9 eV trap concentration was ∼2× higher in the laser-assisted sample, so proton irradiation experiments were conducted to identify the physical source of this level. The results indicated this was a native point defect likely related to gallium interstitials. Overall, this study shows that the laser-assisted MOCVD growth method is promising for future thick, high-quality GaN epilayers after further growth optimizations.

To date, monolithic, epitaxially-integrated III-V/Si tandem solar cells, including the current record-holders, remain limited by excessive threading dislocation densities (TDD) in the metamorphic III-V top cell(s). Our recent development of GaAsyP1-y/Si virtual substrates with TDD in the low-106 cm-2 range paves a pathway toward significant improvement in total device efficiencies for such architectures. In this work, the combination of improved heteroepitaxial processes and growth structures with more optimal subcell design has resulted in a significant increase in GaAs0.75P0.25-on-Si top cell performance. This new subcell now outperforms our previous best by ~4.4% absolute AM1.5G efficiency, with increases in fill factor, JSC, and WOC of about 4.9% absolute, 1.9 mA/cm2, and 0.05 V, respectively.

In this work, we have investigated plasma-assisted deposition of Al2O3 on HVPE (001) β-Ga2O3 and evaluated the dielectric quality from electrical measurements on fabricated metal-oxide-semiconductor (MOS) capacitors. The interface structure and crystallinity of the films were investigated as a function of the growth temperature. The dielectric/semiconductor interfaces were found to have reverse breakdown electric fields up to 5.3 MV/cm in the β-Ga2O3, with relatively low hysteresis in capacitance–voltage and low leakage current. We determined a negative fixed interface charge density at the interface from analysis of thickness-dependent capacitance voltage data. This study shows the advantage of using plasma-assisted deposition to achieve high breakdown strength Al2O3/β-Ga2O3 MOS structures for device application purposes.

Using deep level transient spectroscopy, a baseline defect spectrum for MBE-grown GaAs 0.51 Sb 0.49 on InP was established at optimized and non-optimized growth temperatures. The samples show two dominant traps, with the non-optimized sample having a trap concentration 100-fold greater than the optimized.

Si nanomembranes (NMs) with a thickness of 205 nm were grafted onto GaAsSb/InAlAs layers grown on InP via polydimethylsiloxane (PDMS)-stamp-assisted printing. The Si/GaAsSb heterostructure diodes exhibit promising electrical characteristics, paving the path for GaAsSb-Si integrated photodetectors.

The ability to achieve highly resistive beta-phase gallium oxide (β-Ga2O3) layers and substrates is critical for β-Ga2O3 high voltage and RF devices. To date, the most common approach involves doping with iron (Fe), which generates a moderately deep acceptor-like defect state located at EC-0.8 eV in the β-Ga2O3 bandgap. Recently, there has been growing interest in alternative acceptors, such as magnesium (Mg) and nitrogen (N), due to their predicted deeper energy levels, which could avoid inadvertent charge modulation during device operation. In this work, a systematic study that makes direct correlations between the introduction of N using ion implantation and the observation of a newly observed deep level at EC-2.9 eV detected by deep-level optical spectroscopy (DLOS) is presented. The concentration of this state displayed a monotonic dependence with N concentration over a range of implant conditions, as confirmed by secondary ion mass spectrometry (SIMS). With a near 1:1 match in absolute N and EC-2.9 eV trap concentrations from SIMS and DLOS, respectively, which also matched the measured removal of free electrons from capacitance-voltage studies, this indicates that N contributes a very efficiently incorporated compensating defect. Density functional theory calculations confirm the assignment of this state to be an N (0/−1) acceptor with a configuration of N occupying the oxygen site III [NO(III)]. The near ideal efficiency for this state to compensate free electrons and its location toward the midgap region of the β-Ga2O3 bandgap demonstrates the potential of N doping as a promising approach for producing semi-insulating β-Ga2O3.

The impact of 1.8 MeV proton irradiation on metalorganic chemical vapor deposition grown (010) β-Ga2O3 Schottky diodes is presented. It is found that after a 10.8×1013cm−2 proton fluence the Schottky barrier height of (1.40±0.05 eV) and the ideality factor of (1.05±0.05) are unaffected. Capacitance–voltage extracted net ionized doping curves indicate a carrier removal rate of 268±10cm−1. The defect states responsible for the observed carrier removal are studied through a combination of deep level transient and optical spectroscopies (DLTS/DLOS) as well as lighted capacitance–voltage (LCV) measurements. The dominating effect on the defect spectrum is due to the EC-2.0 eV defect state observed in DLOS and LCV. This state accounts for ∼75% of the total trap introduction rate and is the primary source of carrier removal from proton irradiation. Of the DLTS detected states, the EC-0.72 eV state dominated but had a comparably smaller contribution to the trap introduction. These two traps have previously been correlated with acceptor-like gallium vacancy-related defects. Several other trap states at EC-0.36, EC-0.63, and EC-1.09 eV were newly detected after proton irradiation, and two pre-existing states at EC-1.2 and EC-4.4 eV showed a slight increase in concentration after irradiation, together accounting for the remainder of trap introduction. However, a pre-existing trap at EC-0.40 eV was found to be insensitive to proton irradiation and, therefore, is likely of extrinsic origin. The comprehensive defect characterization of 1.8 MeV proton irradiation damage can aid the modeling and design for a range of radiation tolerant devices.

We report on the design and fabrication of β-Ga2O3 self-aligned lateral MOSFETs by utilizing a heavily doped β-Ga2O3 cap layer. The fabrication of the self-aligned device used a combination of in situ Ga etching for damage free gate recess, in situ growth of Al2O3 for gate dielectric, and atomic layer deposited Al2O3 based sidewall spacers to form highly scaled (<100 nm) source–gate and gate–drain access regions. The fabricated device showed a record high DC drain current density of 560 mA/mm at a drain bias of 5 V. The DC current density was found to be limited by excessive self-heating resulting in premature current saturation in the device. Pulsed I–V measurements of the device showed a record high current density of 895 mA/mm and a high transconductance of 43 mS/mm, thanks to reduced self-heating in the device. The high current densities obtained in this work are promising for the development of high power density devices based on β-Ga2O3.

Gallium Oxide has undergone rapid technological maturation over the last decade, pushing it to the forefront of ultra-wide band gap semiconductor technologies. Maximizing the potential for a new semiconductor system requires a concerted effort by the community to address technical barriers which limit performance. Due to the favorable intrinsic material properties of gallium oxide, namely, critical field strength, widely tunable conductivity, mobility, and melt-based bulk growth, the major targeted application space is power electronics where high performance is expected at low cost. This Roadmap presents the current state-of-the-art and future challenges in 15 different topics identified by a large number of people active within the gallium oxide research community. Addressing these challenges will enhance the state-of-the-art device performance and allow us to design efficient, high-power, commercially scalable microelectronic systems using the newest semiconductor platform.

This study provides the full-bandgap evaluation of defect state distributions in beta phase gallium oxide (β-Ga2O3) grown by low-pressure chemical vapor deposition (LPCVD) on (010) β-Ga2O3 substrates at high growth of up to 20 µm/h. Deep-level optical spectroscopy and deep-level transient spectroscopy measurements applied to Ni/β-Ga2O3 Schottky diodes revealed the presence of a previously unreported defect state at EC-3.6 eV, which dominated the overall trap distribution in LPCVD grown material. However, states at EC-0.8 eV, EC-2.0 eV, and EC-4.4. eV were also detected, similar to prior studies on β-Ga2O3 grown by other methods, with similar or lower concentrations for the LPCVD samples. The EC-0.8 eV and EC-2.0 eV states were previously connected to residual Fe impurities and gallium vacancies, respectively. The total concentration of traps in the LPCVD material was on par with or lower than the state-of-the-art metal–organic chemical vapor deposition-grown materials despite the much higher growth rate, and the distribution of states showed negligible dependence on SiCl4 flow rate and doping concentration. These results demonstrate that the high growth rate of LPCVD-grown β-Ga2O3 is very promising for achieving thick, low defect density, and high-quality layers needed for multi-kV device applications.

Superlattices composed of either monoclinic μ-Fe2O3 or β-(AlxGa1−x)2O3 with β-Ga2O3 spacers are grown on (010) β-Ga2O3 substrates using plasma-assisted molecular beam epitaxy. High-resolution x-ray diffraction data are quantitatively fit using commercial dynamical x-ray diffraction software (LEPTOS) to obtain layer thicknesses, strain, and compositions. The strain state of β-(AlxGa1−x)2O3 and μ-Fe2O3 superlattices as characterized using reciprocal space maps in the symmetric (020) and asymmetric (420) diffraction conditions indicates coherent growths that are strained to the (010) β-Ga2O3 lattice. β-(AlxGa1−x)2O3 and μ-Fe2O3 superlattices grown at hotter substrate temperatures result in crystal structures with better coherency and reduced defects compared to colder growths. The growth rate of μ-Fe2O3 is ∼2.6 nm/min at Tsub = 700 °C and drops to ∼1.6 nm/min at Tsub = 800 °C due to increased Fe interdiffusion at hotter substrate temperatures. Scanning transmission electron microscopy data of a μ-Fe2O3 superlattice grown at Tsub = 700 °C confirm that there is significant diffusion of Fe atoms into β-Ga2O3 layers.