Single-crystal growth of (100) beta-Ga2O3 and the attempt to grow GaP on it by hydride vapor phase epitaxy (HVPE) is been described. The phase purity and (100) orientation of the crystal is confirmed by X-ray diffraction (XRD). The selected area electron diffraction pattern confirms the monoclinic structure with a C2/m space group of beta-Ga2O3. Raman results reveal the stretching and bending vibrations of Ga-O and Ga-O-Ga octahedrons, respectively. The wafer exhibits approximate to 80% optical transmission and surface roughness of approximate to 5 nm. GaP layers are grown on (100)-oriented beta-Ga2O3 substrates by HVPE. The GaP/beta-Ga2O3 heterostructures are characterized using XRD and Raman spectroscopy. Diffraction peak at (111) confirms the zinc blende phase of GaP. The longitudinal optical (405 cm-1) and transverse optical (368 cm-1) phonon modes in the Raman spectra confirm the crystalline GaP. Further optimization is expected to enhance the crystalline quality of the GaP layer on the Ga2O3 wafer. The potential of GaP/(100) beta-Ga2O3 heterostructures are highlighted.

MXene is a promising energy storage material for miniaturized microbatteries and microsupercapacitors (MSCs). Despite its superior electrochemical performance, only a few studies have reported MXene-based ultrahigh-rate (>1000 mV s−1) on-paper MSCs, mainly due to the reduced electrical conductance of MXene films deposited on paper. Herein, ultrahigh-rate metal-free on-paper MSCs based on heterogeneous MXene/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)-stack electrodes are fabricated through the combination of direct ink writing and femtosecond laser scribing. With a footprint area of only 20 mm2, the on-paper MSCs exhibit excellent high-rate capacitive behavior with an areal capacitance of 5.7 mF cm−2 and long cycle life (>95% capacitance retention after 10,000 cycles) at a high scan rate of 1000 mV s−1, outperforming most of the present on-paper MSCs. Furthermore, the heterogeneous MXene/PEDOT:PSS electrodes can interconnect individual MSCs into metal-free on-paper MSC arrays, which can also be simultaneously charged/discharged at 1000 mV s−1, showing scalable capacitive performance. The heterogeneous MXene/PEDOT:PSS stacks are a promising electrode structure for on-paper MSCs to serve as ultrafast miniaturized energy storage components for emerging paper electronics. 

Herein, the fabrication of hybrid InP/Si 1.55 μm range photonic‐crystal surface‐emitting lasers (PCSELs) using micro‐transfer printing is reported on. This fabrication technology is expected to have important advantages in manufacturing, performance, and silicon integration, but it relies on a fine‐tuned process for selective etching, release, and subsequent printing of active InP membranes on top of a Si photonic‐crystal layer. Herein, the appropriate wet etching chemistry and processing methodology for preserved layer and interface integrity are discussed and the technology by optically pumped PCSELs is demonstrated, showing continuous‐wave operation at room temperature.

The growing demands of sustainable, portable, and wearable electronics pose new demands on miniaturized energy storage devices that can be integrated on flexible substrates such as paper. Microsupercapacitors (MSCs), especially MXene-based pseudocapacitive MSCs with fast charging/discharging rate, high power density, and long cycle life, are competitive candidates as power supply for emerging flexible and wearable on-paper electronics. However, few studies have reported MXene-based on-paper MSCs to simultaneously attain ultrahigh-rate (>1000 mV s⁻¹) capability and large areal capacitance >10 mF cm⁻². Herein, ultrafast metal-free on-paper MSCs are fabricated through leveraging the synergistic effect of conductive PEDOT:PSS and capacitive MXene (Ti₂C) to achieve a remarkable areal capacitance of 30 mF cm⁻² and long lifetime (>96% capacitance retention after 10 000 cycles) at an ultrahigh scan rate of 1000 mV s⁻¹, outperforming most of the present on-paper or MXene-containing MSCs. Moreover, the printed on-paper metal-free MSC arrays attain extended working voltage window of up to 6 V and outstanding capacitive performance at an ultrahigh scan rate of 10 V s⁻¹. The on-paper PEDOT:PSS-Ti₂C composite MSCs offer new opportunities as eco-friendly microscale power sources for emerging paper-based portable and wearable electronics.

GaAsP/Si with high crystalline quality fabricated by cost-effective heteroepitaxial technology is a promising pathway for realizing low-cost Si-based tandem solar cell with efficiency higher than 30%. Herein, hydride vapor-phase epitaxy is used to perform selective area growth of GaAsP with high lateral coverage, referred to as epitaxial lateral overgrowth (ELOG). The ELOG is performed on GaAs-based substrates as a prestudy, followed by GaAs/Si and GaAsP/Si seed wafers employing chemical mechanical polishing to fabricate full 2 00 GaAsP/Si templates. These are subsequently used to grow and process GaAsP/Si pn-junction structures for electrical characterization. The ELOG GaAsP is studied by spatially resolved photoluminescence (PL) mapping and high-resolution X-ray diffraction measurements. PL analysis of the GaAsP/GaAs ELOG samples reveals an enhanced P-incorporation during lateral growth of GaAsP. This is also observed for the GaAsP/Si ELOG templates along with evidence of improved material quality, clearly distinguishing the laterally grown GaAsP from the planar growth directly above the Si substrate. Leakage pathways causing reduced electrical performance of the ELOG GaAsP/Si pn-junction structures are identified.

Orientation-patterned gallium phosphide (OP-GaP) has been grown heteroepitaxially on OP gallium arsenide (GaAs) templates using hydride vapor phase epitaxy (HVPE). The effect of OP-GaAs template fabrication methods of epitaxial-inversion and wafer bonding on the heteroepitaxial OP-GaP growth has been investigated. OP-GaP layers with a growth rate of up to 35 mu m/h and excellent domain fidelity were obtained. The growth rate and the domain fidelity have been revealed/studied by scanning electron microscope (SEM). In addition, we demonstrate that the crystalline quality of the individual domains, namely, the substrate-oriented domains (ODs) and the inverted domains (IDs), can be investigated by high-resolution x-ray diffraction reciprocal space mapping (HRXRDRSM), which can also indicate the domain fidelity. Attempts to increase the growth rate and improve the domain fidelity by increasing the III and V group precursors resulted in either an increase in the growth rate in the OP-GaP layers grown on epitaxial inversion OP-GaAs template at the expense of the domain crystalline quality and fidelity or an improvement in the crystalline quality of the domains at the expense of the growth rate in the OP-GaP layers grown on wafer-bonded OP-GaAs templates. In the case of OP-GaP grown on OP-GaAs templates prepared by epitaxial inversion, the crystalline quality of the ODs is better than that of the IDs, but it shows that the quality of the inverted layer in the template influences the quality and fidelity of the grown domains. To the authors' knowledge, exploitation of HRXRDRSM studies on OP-GaP to establish the crystalline quality of its individual domains (ODs and IDs) is the first of its kind. OP-ZnSe grown on OP-GaAs templates has also been included in this study to further emphasize the potential of this method. We propose from this study that once the growth rate is optimized from SEM studies, HRXRDRSM analysis alone can be used to assess the structural quality and to infer the domain fidelity of the OP structures.

Terahertz quantum cascade laser sources based on intra-cavity Cherenkov difference-frequency generation in dual-wavelength mid-infrared quantum cascade lasers are currently the only monolithic semiconductor laser technology that can deliver continuous-wave coherent terahertz output at room temperature. Because the Cherenkov difference-frequency generation process enables terahertz radiation generation and extraction across a wide range of frequencies, it is often assumed that phase-matching conditions for this process are automatically fulfilled. We theoretically analyze and experimentally demonstrate that phase-matching plays an important role in these devices, and significant improvements in terahertz power output can be achieved by adjusting the waveguide configuration of the quantum cascade lasers to provide better phase-matching.

Buried heterostructure quantum cascade lasers (BH-QCLs) operating at high temperature in mid-infrared (MIR) to THz spectral range are desired for chemical sensing and free-space optical communication (FOC). In this work, Fe doped semi-insulating InP (SI-InP) regrowth is demonstrated in a hydride vapor phase epitaxy (HVPE) reactor for advanced MIR and THz BH-QCLs grown by MBE and MOCVD. SI-InP regrowth is implemented in THz QCL pillar arrays and narrow width and reverse-taper MIR BH-QCLs for efficient heat dissipation. By exploiting SI-InP regrowth, the parasitic capacitance in MIR distributed feedback BH-QCL can be suppressed, which is exploited for high speed FOC application.

High crystal quality GaAsP/Si fabricated by cost effective heteroepitaxial technology is promising to realize low-cost Si based tandem solar cell with efficiency higher than 30%. In this work, epitaxial lateral overgrowth (ELOG) of GaAsP/GaAs and GaAsP/GaAs/Si by hydride vapor phase epitaxy (HVPE) and their properties are studied by photoluminescence (PL) mapping. High crystal quality ELOG GaAsP/Si is obtained with enhanced PL intensity and narrow line width indicating reduced defect density provided by ELOG approach.

Heteroepitaxial Zn-doped p-GaP was grown on (001) GaAs, (001) Si and (111) Si substrates by hydride vapor phase epitaxy for solar-driven photoelectrochemical applications of hydrogen generation by water splitting and CO2 reduction. Growth of GaP on Si was realized through the implementation of a low-temperature buffer layer, and the morphology and crystalline quality were enhanced by optimizing the precursor flows and pre-heating ambient substrate. The p-GaP/GaAs and p-GaP/Si samples were processed to photoelectrodes with an amorphous TiO2 coating for CO2 reduction and a combination of TiO2 layer and mesoporous tungsten phosphide catalyst for water splitting. P-GaP/GaAs with suitable Zn-doping concentration exhibited photoelectrochemical performance comparable to homoepitaxial p-GaP/GaP for water splitting and CO2 reduction. Degradation of photocurrent in p-GaP/Si photoelectrodes is observed in PEC water splitting due to the high density of defects arising from heteroepitaxial growth.