ABSTRACT
In this work, nanoplasmonically enhanced α-Ga2O3 solar-blind photodetectors with an interdigital structure were fabricated on sapphire. By introducing Al nanoparticles (NPs) onto the device surface, the photodetector obtained a significant increase in responsivity at the solar-blind region, and the response peak located at 244 nm reached 3.36 A/W under an applied voltage of 5 V. Compared with the responsivity at 320 nm, the response ratio exceeds 240, demonstrating a superior solar-blind cut-off edge. It also presents that the photocurrent was dramatically increased under 254 nm ultraviolet irradiation for the enhanced device while the dark current remains below 1 pA at 20 V. To explicitly elucidate the enhancement effects by Al NPs under ultraviolet illumination, Kelvin probe force microscopy was employed and directly revealed the physical mechanism of surface plasmon oscillation, which promoted the formation of localized electric fields on α-Ga2O3. In addition, we illustrated the effects of interdigital spacing on device performances through experimental measurements and theoretical calculations. These results not only provide direct evidences for Al nanoplasmonic enhancement on the α-Ga2O3 device but also facilitate design and fabrication of solar-blind photodetectors.
ABSTRACT
Implementing selective-area p-type doping through ion implantation is the most attractive choice for the fabrication of GaN-based bipolar power and related devices. However, the low activation efficiency of magnesium (Mg) ions and the inevitable surface decomposition during high-temperature activation annealing process still limit the use of this technology for GaN-based devices. In this work, we demonstrate successful p-type doping of GaN using protective coatings during a Mg ion implantation and thermal activation process. The p-type conduction of GaN is evidenced by the positive Seebeck coefficient obtained during thermopower characterization. On this basis, a GaN p-i-n diode is fabricated, exhibiting distinct rectifying characteristics with a turn-on voltage of 3 V with an acceptable reverse breakdown voltage of 300 V. Electron beam induced current (EBIC) and electroluminescent (EL) results further confirm the formation of p-type region due to Mg ion implantation and subsequent thermal activation. This repeatable and uniform manufacturing process can be implemented in mass production of GaN devices for versatile power and optoelectronic applications.
ABSTRACT
To suppress noise from full daylight background or environmental radiation, a spectrally selective solar-blind photodetector is widely required in many applications that need detection of light within a specific spectral range. Here, we present highly narrow-band solar-blind photodetectors by light polarization engineering of the anisotropic transitions in ß-Ga2O3 single crystals. The polarized transmittance characteristics reveal that direct transitions from valance subbands to the conduction band minimum are tuned between 4.53 and 4.76 eV for the light polarized E// c and E// b. The polarization-dependent photoresponsivity verifies that the order of fundamental band-to-band transitions obeys well the selection rules in terms of the valence-band splitting in the ß-Ga2O3 monoclinic crystal band structure. By combining an orthogonally aligned identical ß-Ga2O3 (100) single crystal filter with a detector measured at a chopper frequency of 17 Hz, a highly narrow-band detection is produced with a peak responsivity of 0.23 A/W at 262 nm, an EQE of 110%, a bandwidth of 10 nm, a light rejection ratio over 800, and a response time of 0.86 ms. This provides a new paradigm for a narrow-band solar-blind photodetector with broad applications where background noise emission needs to be suppressed.
ABSTRACT
The ability to manipulate light-matter interaction in semiconducting nanostructures is fascinating for implementing functionalities in advanced optoelectronic devices. Here, we report the tailoring of radiative emissions in a ZnTe/ZnTe:O/ZnO core-shell single nanowire coupled with a one-dimensional aluminum bowtie antenna array. The plasmonic antenna enables changes in the excitation and emission processes, leading to an obvious enhancement of near band edge emission (2.2 eV) and subgap excitonic emission (1.7 eV) bound to intermediate band states in a ZnTe/ZnTe:O/ZnO core-shell nanowire as well as surface-enhanced Raman scattering at room temperature. The increase of emission decay rate in the nanowire/antenna system, probed by time-resolved photoluminescence spectroscopy, yields an observable enhancement of quantum efficiency induced by local surface plasmon resonance. Electromagnetic simulations agree well with the experimental observations, revealing a combined effect of enhanced electric near-field intensity and the improvement of quantum efficiency in the ZnTe/ZnTe:O/ZnO nanowire/antenna system. The capability of tailoring light-matter interaction in low-efficient emitters may provide an alternative platform for designing advanced optoelectronic and sensing devices with precisely controlled response.
ABSTRACT
Wide-bandgap inorganic semiconductors based ultraviolet lasers bring versatile applications with significant advantages including low-power consumption, high-power output, robustness and long-term operation stability. However, flexible membrane lasers remain challenging predominantly due to the need for a lattice matched supporting substrate. Here, we develop a simple laser liftoff process to make freestanding single crystalline ZnO membranes that demonstrate low-threshold ultraviolet stimulated emissions together with large sized dimension (> 2 mm), ultralow-weight (m/A<15 g/m2) and excellent flexibility. The 2.6 µm-thick crack-free ZnO membrane exhibits well-retained single crystallinity and enhanced excitonic emissions while the defect-related emissions are completely suppressed. The inelastic exciton-exciton scattering stimulated emissions with increased spontaneous emission rate is obtained with a reduced threshold of 0.35 MW/cm2 in the ZnO membrane transferred onto a flexible polyethylene naphthalate substrate. Theoretical simulations reveal that it is a synergetic effect of the increased quantum efficiency via Purcell effect and the improved optical gain due to vertical directional waveguiding of the membrane, which functions as a Fabry-Perot photonic resonator due to the refractive index contrast at ZnO-air boundaries. With simple architecture, efficient exciton recombination and easy fusion with waveguide system, the ZnO membranes provide an alternative platform to develop compact low-threshold ultraviolet excitonic lasers.
ABSTRACT
The metastable α-phase Ga2O3 is an emerging material for developing solar-blind photodetectors and power electronic devices toward civil and military applications. Despite its superior physical properties, the high quality epitaxy of metastable phase α-Ga2O3 remains challenging. To this end, single crystalline α-Ga2O3 epilayers are achieved on nonpolar ZnO (112Ì 0) substrates for the first time and a high performance Au/α-Ga2O3/ZnO isotype heterostructure-based Schottky barrier avalanche diode is demonstrated. The device exhibits self-powered functions with a dark current lower than 1 pA, a UV/visible rejection ratio of 103 and a detectivity of 9.66 × 1012 cm Hz1/2 W-1. Dual responsivity bands with cutoff wavelengths at 255 and 375 nm are observed with their peak responsivities of 0.50 and 0.071 A W-1 at -5 V, respectively. High photoconductive gain at low bias is governed by a barrier lowing effect at the Au/Ga2O3 and Ga2O3/ZnO heterointerfaces. The device also allows avalanche multiplication processes initiated by pure electron and hole injections under different illumination conditions. High avalanche gains over 103 and a low ionization coefficient ratio of electrons and holes are yielded, leading to a total gain over 105 and a high responsivity of 1.10 × 104 A W-1. Such avalanche heterostructures with ultrahigh gains and bias-tunable UV detecting functionality hold promise for developing high performance solar-blind photodetectors.
ABSTRACT
Intermediate band solar cells (IBSCs) are conceptual and promising for next generation high efficiency photovoltaic devices, whereas, IB impact on the cell performance is still marginal due to the weak absorption of IB states. Here a rational design of a hybrid structure composed of ZnTe:O/ZnO core-shell nanowires (NWs) with Al bowtie nanoantennas is demonstrated to exhibit strong ability in tuning and enhancing broadband light response. The optimized nanowire dimensions enable absorption enhancement by engineering leaky-mode dielectric resonances. It maximizes the overlap of the absorption spectrum and the optical transitions in ZnTe:O intermediate-band (IB) photovoltaic materials, as verified by the enhanced photoresponse especially for IB states in an individual nanowire device. Furthermore, by integrating Al bowtie antennas, the enhanced exciton-plasmon coupling enables the notable improvement in the absorption of ZnTe:O/ZnO core-shell single NW, which was demonstrated by the profound enhancement of photoluminescence and resonant Raman scattering. The marriage of dielectric and metallic resonance effects in subwavelength-scale nanowires opens up new avenues for overcoming the poor absorption of sub-gap photons by IB states in ZnTe:O to achieve high-efficiency IBSCs.
