GaN microwires were shown to possess promising characteristics as building blocks for radiation resistant particle detectors. They were grown by metal organic vapour phase epitaxy with diameters between 1 and 2 μm and lengths around 20 μm. Devices were fabricated by depositing gold contacts at the extremities of the wires using photolithography. The response of these single wire radiation sensors was then studied under irradiation with 2 MeV protons. Severe degradation of the majority of devices only sets in for fluences above protons cm−2 revealing good radiation resistance. During proton irradiation, a clear albeit small current gain was observed with a corresponding decay time below 1 s. Photoconductivity measurements upon irradiation with UV light were carried out before and after the proton irradiation. Despite a relatively low gain, attributed to significant dark currents caused by a high dopant concentration, fast response times of a few seconds were achieved comparable to state-of-the-art GaN nanowire photodetectors. Irradiation and subsequent annealing resulted in an overall improvement of the devices regarding their response to UV radiation. The photocurrent gain increased compared to the values that were obtained prior to the irradiation, without compromising the decay times. The results indicate the possibility of using GaN microwires not only as UV detectors, but also as particle detectors.
Europium (Eu)-implanted AlN nanowire (NW) p–n junctions, subjected to rapid thermal annealing at 1000 °C, were investigated in view of application as red light-emitting diodes (LEDs). In a first step, the structural and optical properties of NWs implanted with two different fluences (1 × 1014 cm–2 and 5 × 1014 cm–2) were studied. The luminescence of the trivalent Eu ions (Eu3+) was achieved for both samples using below and above AlN bandgap energy excitation. The excitation below the AlN bandgap occurs through two broad bands, A1 (peaked at ∼270 nm) and A2 (peaked at ∼367 nm), associated with lattice defects. In addition to Eu3+ luminescence, other radiative channels linked to deep-level defects were identified in photoluminescence (PL). The cathodoluminescence (CL) relative intensity ratio between intra-ionic and defect-related emissions increases compared to that of PL. In both PL and CL, the Eu3+ luminescence intensity increases about three times for the highest fluence, while the contribution from radiative recombination at defects decreases. This study also allowed to map an in-depth profile of the optically active Eu3+, revealing that it extends deeper than the range predicted by Monte Carlo simulations. Based on these findings, a proof-of-concept red LED is shown using the NWs implanted with the highest fluence. The devices exhibited the typical rectifying behavior of a p–n junction and an electroluminescence signal dominated by the 5D0 → 7F2 transition (∼624 nm) starting at a threshold voltage of 12 V. The demonstration of red LEDs based on Eu-implanted AlN NWs highlights the potential of such an approach for developing multi-color nano-emitters.
Self-powered particle detectors have the potential to offer exceptional flexibility and compactness in applications where size limits and low power consumption are key requisites. Here, we report on the fabrication and characterization of radiation sensors based on GaN core/shell p–n junction microwires working without externally applied bias. With their small size, high resistance to radiation, and high crystalline quality, GaN microwires constitute highly interesting building blocks for radiation-hard devices. Through microfabrication steps, single-wire devices were processed that show a leakage current as low as 1 pA in reverse bias. Irradiation with both UV light and 2 MeV protons results in photo/ionocurrent signals several orders of magnitude above the dark current and response times below 30 ms. The sensor also showed a good resistance to radiation. Although we observed a small increase in the leakage current after a prolonged proton irradiation, the measured transient ionocurrent signal remains stable during irradiation with a total proton fluence of at least 1×1016 protons/cm2.
GaN is a wide bandgap semiconductor which is expected to withstand high radiation doses. Consequently, it is considered a promising material for new generation particle detectors in radiation related applications. We report on the fabrication and electrical characterization under proton irradiation of single microwire sensors based on a back-to-back Schottky contact configuration. The microwires are grown by metal-organic vapor phase epitaxy and processed into sensors by using optical lithography on dispersed wires. We investigate the impact of the contacts and the semiconductor bulk on the ion beam induced current (IBIC) by irradiating specific areas of the sensor and simultaneously measuring the change in conductivity. We observed that the contribution of the excess charge carriers generated in the depletion regions formed at the contact interfaces is of low influence when compared to the excess charge carriers generated in the microwire bulk.
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