Hong Yeol Kim

Dependence on proton energy of degradation of AlGaN/GaN high electron mobility transistors

The effects of proton irradiation energy on dc, small signal, and large signal rf characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. AlGaN/GaN HEMTs were irradiated with protons at fixed fluence of 5 × 1015/cm2 and energies of 5, 10, and 15 MeV. Both dc and rf characteristics revealed more degradation at lower irradiation energy, with reductions of maximum transconductance of 11%, 22%, and 38%, and decreases in drain saturation current of 10%, 24%, and 46% for HEMTs exposed to 15, 10, and 5 MeV protons, respectively. The increase in device degradation with decreasing proton energy is due to the increase in linear energy transfer and corresponding increase in nonionizing energy loss with decreasing proton energy in the active region of the HEMTs. After irradiation, both subthreshold drain leakage current and reverse gate current decreased more than 1 order of magnitude for all samples. The carrier removal rate was in the range 121–336 cm−1 over the range of proton energies employed in this study.

Effects of proton irradiation energies on degradation of AlGaN/GaN high electron mobility transistors

The authors report the proton energy dependence of the degradation of AlGaN/GaN high electron mobility transistors (HEMTs) with GaN cap layers from 5 to 15 MeV at a fixed dose of 5 × 1015 cm−2. All the samples degraded after proton irradiation. However, higher damage in dc electrical properties was observed at lower proton energies. Saturation currents at VDS = 6 V and VGS = 0 V reduced by 47% after proton irradiation at 5 MeV energy, but the reduction was less by 25% and 9% at 10 and 15 MeV, respectively. Similar trends were observed in other electrical properties [transconductance (gm) and gate leakage currents]. This energy dependence from 5 to 15 MeV can be explained by the energy-dependent penetration depth of the proton. Protons with higher kinetic energy can penetrate deeper while creating less numbers of defects at shallow depths where the active layers of the HEMTs are located. These results are in good agreement with stopping and range of ions in matter results. The optimization of the AlGaN/GaN...

Effect of neutron irradiation on electrical and optical properties of InGaN/GaN light-emitting diodes

InGaN/GaN multiquantum well light-emitting diodes (LED) with emission wavelength of 450 nm were irradiated with average energy of 9.8 MeV and dose of 5.5×1011 cm−2 neutrons. Right after irradiation, the forward current of the irradiated LEDs was decreased as a result of the creation of deep levels by the neutron-induced lattice displacement. However, unstable lattice damages resulting from the collisions with the incoming neutrons were removed at room temperature 6 days after the irradiation. The diode turn-on voltage, ideality factor, and optical emission intensity were recovered to preirradiated state by self-annealing process at room temperature.

GaN-based ultraviolet light-emitting diodes with AuCl 3 -doped graphene electrodes

We demonstrate AuCl3-doped graphene transparent conductive electrodes integrated in GaN-based ultraviolet (UV) light-emitting diodes (LEDs) with an emission peak of 363 nm. AuCl3 doping was accomplished by dipping the graphene electrodes in 5, 10 and 20 mM concentrations of AuCl3 solutions. The effects of AuCl3 doping on graphene electrodes were investigated by current-voltage characteristics, sheet resistance, scanning electron microscope, optical transmittance, micro-Raman scattering and electroluminescence images. The optical transmittance was decreased with increasing the AuCl3 concentrations. However, the forward currents of UV LEDs with p-doped (5, 10 and 20 mM of AuCl3 solutions) graphene transparent conductive electrodes at a forward bias of 8 V were increased by ~48, 63 and 73%, respectively, which can be attributed to the reduction of sheet resistance and the increase of work function of the graphene. The performance of UV LEDs was drastically improved by AuCl3 doping of graphene transparent conductive electrodes.

Selective chemical etch of gallium nitride by phosphoric acid

The authors report on the direct comparison of the chemical etch characteristics on both Ga- and N-face gallium nitride (GaN) by phosphoric acid. First, Ga-face GaN was grown next to N-face GaN by a polarity inversion method in a metal-organic chemical vapor deposition reactor. Micro-photoluminescence, atomic force microscopy, scanning electron microscopy, and micro-Raman spectroscopy were used to analyze the etch characteristics of Ga- and N-face GaN before and after a H3PO4-based chemical etch. Ga-face was chemically stable in a phosphoric acid solution. However, the chemical etch continued proceeding on the N-face GaN due to the weak repulsive force to OH− ions. Dodecagonal nano-pyramids which dramatically enhanced the photoluminescence intensity were observed on N-face GaN after a H3PO4-based chemical etch.

AlGaN/GaN High Electron Mobility Transistors Irradiated with 17 MeV Protons

AlGaN/GaN high electron mobility transistors (HEMTs) with GaN cap layers were irradiated with high-energy (17 MeV) protons to doses up to 2 X 10 16 cm -2 . There was no significant degradation in dc electrical parameters such as drain-source current (I DS ) and extrinsic transconductance (g m ) of the HEMTs up to a fluency of 7.2 X 10 13 protons/cm 2 . At the highest dose of 2 X 10 16 protons/cm 2 there was a decrease of 43% in I DS and a 29% decrease in g m . The data are consistent with the introduction of defect centers in the HEMT structure by the high-energy protons leading to a reduction in carrier concentration and mobility in the two-dimensional electron gas channel. These results show that AlGaN/GaN HEMTs are attractive for space-based applications where high-energy proton fluxes are present.

Impact of proton irradiation on dc performance of AlGaN/GaN high electron mobility transistors

The effects of high energy proton irradiation dose on dc performance as well as critical voltage of the drain-voltage step-stress of AlGaN/GaN high electron mobility transistors (HEMTs) were investigated to evaluate the feasibility of AlGaN/GaN HEMTs for space applications, which need to stand a variety of irradiations. The HEMTs were irradiated with protons at a fixed energy of 5 MeV and doses ranging from 109 to 2 × 1014 cm−2. For the dc characteristics, there was only minimal degradation of saturation drain current (IDSS), transconductance (gm), electron mobility, and sheet carrier concentration at doses below 2 × 1013 cm−2, while the reduction of these parameters were 15%, 9%, 41% and 16.6%, respectively, at a dose of 2 × 1014 cm−2. At this same dose condition, increases of 37% in drain breakdown voltage (VBR) and of 45% in critical voltage (Vcri) were observed. The improvements of drain breakdown voltage and critical voltage were attributed to the modification of the depletion region due to the intro...

GaN-based ultraviolet light-emitting diodes with AuCl3-doped graphene electrodes

We demonstrate AuCl3-doped graphene transparent conductive electrodes integrated in GaN-based ultraviolet (UV) light-emitting diodes (LEDs) with an emission peak of 363 nm. AuCl3 doping was accomplished by dipping the graphene electrodes in 5, 10 and 20 mM concentrations of AuCl3 solutions. The effects of AuCl3 doping on graphene electrodes were investigated by current-voltage characteristics, sheet resistance, scanning electron microscope, optical transmittance, micro-Raman scattering and electroluminescence images. The optical transmittance was decreased with increasing the AuCl3 concentrations. However, the forward currents of UV LEDs with p-doped (5, 10 and 20 mM of AuCl3 solutions) graphene transparent conductive electrodes at a forward bias of 8 V were increased by ~48, 63 and 73%, respectively, which can be attributed to the reduction of sheet resistance and the increase of work function of the graphene. The performance of UV LEDs was drastically improved by AuCl3 doping of graphene transparent conductive electrodes.

Study on the effects of proton irradiation on the dc characteristics of AlGaN/GaN high electron mobility transistors with source field plate

The effects of proton irradiation dose on the dc characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) with source field plates were studied. The HEMTs were irradiated with various protons doses ranging from 5 × 1012 to 5 × 1015 cm−2 at a fixed energy of 5 MeV. HEMTs irradiated with proton dose below 5 × 1013 cm−2 showed less than 2% degradation of either saturation drain current (IDSS) or transconductance (gm). Significant changes of these parameters were observed for the devices irradiated with doses above 5 × 1013 cm−2. HEMTs irradiated with the highest proton dose of 5 × 1015 cm−2 showed a reduction of IDSS and gm of 86% and 64.7%, and a positive Vth shift of 0.84 V, respectively. Despite the significant IDSS and gm reductions, the off-state drain breakdown voltage (VBR) was improved more than five times at this particular irradiation condition. The significant improvement of off-state drain breakdown voltage was attributed to the formation of a virtual gate at drain side of gate edge, which was the result of the generation of defect centers at AlGaN/GaN interface.

Proton irradiation energy dependence of dc and rf characteristics on InAlN/GaN high electron mobility transistors

The effects of proton irradiation energy on dc and rf characteristics of InAlN/GaN high electron mobility transistors (HEMTs) were investigated. A fixed proton dose of 5 × 1015 cm−2 with 5, 10, and 15 MeV irradiation energies was used in this study. For the dc characteristics, degradation was observed for sheet resistance, transfer resistance, contact resistivity, saturation drain current, maximum transconductance, reverse-bias gate leakage current, and sub-threshold drain leakage current for all the irradiated HEMTs; however, the degree of the degradation was decreased as the irradiation energy increased. Similar trends were obtained for the rf performance of the devices, with ∼10% degradation of the unity gain cut-off frequency (fT) and maximum oscillation frequency ( fmax) for the HEMTs irradiated with 15 MeV protons but 30% for 5 MeV proton irradiation. The carrier removal rate was in the range 0.66–1.24 cm−1 over the range of proton energies investigated.