P-type conversion of n−-GaN by Mg-ion implantation was successfully performed using high quality GaN epitaxial layers grown on free-standing low-dislocation-density GaN substrates. These samples ...showed low-temperature PL spectra quite similar to those observed from Mg-doped MOVPE-grown p-type GaN, consisting of Mg related donor–acceptor pair (DAP) and acceptor bound exciton (ABE) emission. P–n diodes fabricated by the Mg-ion implantation showed clear rectifying I–V characteristics and UV and blue light emissions were observed at forward biased conditions for the first time.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The effect of the surface off‐angle toward either the a‐ or m‐axis on the defect formation is characterized using deep‐level transient spectroscopy (DLTS) in conjunction with the carrier ...concentration for Ni Schottky contacts formed on n‐GaN drift layers. In both noncontact and conventional capacitance–voltage results, off‐angle dependence on carrier concentration is observed. For all samples, a large dominant peak appears at approximately 270 K in the DLTS spectra and is attributed to E3 (EC − 0.57–0.61 eV) defects. Carbon atoms can act as carrier compensators and form E3 defects. These results can be interpreted based on how C incorporation during crystal growth depends on the off‐angle.
The effect of the surface off‐angle toward either the a‐ or m‐axis on the defect formation is characterized using deep‐level transient spectroscopy for Ni Schottky contacts formed on n‐GaN drift layers. A large dominant peak appears at 270 K and is attributed to E3 defects. Carbon atoms can act as carrier compensators and form E3 defects.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Photo-electrochemical (PEC) etching was used to fabricate deep trench structures in a GaN-on-GaN epilayer grown on n-GaN substrates. A 50-nm-thick layer of Ti used for an etching mask was not removed ...even after etching to a depth of >30 µm. The width of the side etching was less than 1 µm with high accuracy. The aspect ratio (depth/width) of a 3.3-µm-wide trench with a PEC etching depth of 24.3 µm was 7.3. These results demonstrate the excellent potential of PEC etching for fabricating deep trenches in vertical GaN devices.
We report the electrical characteristics of Schottky contacts with nine different metals (Ag, Ti, Cr, W, Mo, Au, Pd, Ni, and Pt) formed on clean m-plane surfaces by cleaving freestanding GaN ...substrates, compared with these of contacts on Ga-polar c-plane n-GaN surfaces grown on GaN substrates. The n-values from the forward current-voltage (I-V) characteristics are as good as 1.02-1.18 and 1.02-1.09 for the m- and c-plane samples, respectively. We found that the reverse I-V curves of both samples can be explained by the thermionic field emission theory, and that the Schottky barrier height of the cleaved m-plane contacts shows a metal work function dependence.
Electron traps in n-GaN layers with a relatively low-free-carrier-concentration of approximately 1 × 1016 cm−3 were characterized by deep-level transient spectroscopy. Sample layers were grown by ...metal organic chemical vapor deposition with a thickness of 12 µm on freestanding GaN substrates, and were doped with both silicon and carbon. The measurement results showed a reduction in the density of carbon-related electron traps at an energy level of EC −0.40 eV in GaN on GaN samples, compared with GaN on SiC samples. It was also observed that the doping of carbon significantly suppressed electron traps at EC −0.61 eV, which was associated with the nitrogen antisite. Consequently, the possibility of minimizing all of the electron traps located between EC −0.19 and −0.89 eV in n-GaN was demonstrated by controlling the carbon doping in the nitrogen site.
Abstract
We applied scanning internal photoemission microscopy (SIPM) to clarify the electrical characteristics on the electrode periphery of Ni/n-GaN Schottky contacts. Two types of Schottky ...contacts with different electrode formation methods were prepared. For the samples in which the Ni contacts were evaporated through a metal shadow mask, in the scanning electron microscopes (SEM) observation, the electrode edges were tailed and the tail was divided into two contrasts, a bright region with a width of 15.5
μ
m from the electrode edge followed by a dark region with a width of 32
μ
m. The SIPM signal was obtained from the first 16
μ
m tailing region, and corresponded with the SEM images. For the photolithography sample, a sharp edge less than 1
μ
m wide was obtained and no increase in SIPM signal was detected on the edge. These results indicate SIPM is able to characterize the electrical properties of electrode periphery in conjunction with the structural characteristics.
In this letter, we describe the characteristics of Gallium Nitride (GaN) p--n junction diodes fabricated on free-standing GaN substrates with low specific on-resistance $R_{\text{on}}$ and high ...breakdown voltage $V_{\text{B}}$. The breakdown voltage of the diodes with the field-plate (FP) structure was over 3 kV, and the leakage current was low, i.e., in the range of $10^{-4}$ A/cm 2 . The specific on-resistance of the diodes of 60 μm diameter with the FP structure was 0.9 m$\Omega$$\cdot$cm 2 . Baliga's figure of merit ($V_{\text{B}}{}^{2}/R_{\text{on}}$) of 10 GW/cm 2 is obtained. Although a certain number of dislocations were included in the device, these excellent results indicated a definite availability of this material system for power-device applications.
We applied scanning internal photoemission microscopy (SIPM) to characterize the degradation of GaN Schottky contacts formed on a thick n-GaN layer grown on a freestanding GaN substrate by in situ ...applying reverse bias voltage (Vbias) down to −45 V. For most of the contacts, uniform distribution of the photocurrent was observed over the electrode with the visible lasers. Irregular-shape regions with 5%-25% larger photocurrent appeared with the near UV laser by applying Vbias, but the I-V characteristics were stable. On the other hand, for the contacts with a slightly larger reverse current, the photocurrent distribution was also uniform at Vbias = 0 V, but over Vbias = −36 V, the photocurrent was intensively increased at small spots. After the SIPM measurements, the I-V characteristics became leaky, and the same spots were observed in the microscope image. These results indicate that SIPM is useful for in situ monitoring of the initial stage of the degradation under applying reverse bias voltage.
Abstract
We present the experimental results on the mapping characterization of n-type GaN Schottky contacts with selective contactless photoelectrochemical (CL-PEC) etching by using scanning ...internal photoemission microscopy (SIPM). The CL-PEC etching was performed in four kinds of aqueous solutions (KOH mixed with K
2
S
2
O
8
(oxidant), phosphoric acid mixed with oxidant, only oxidant, and ammonia). The Schottky barrier height (
qϕ
B
) values decreased by less than 0.1 eV in the etching with the KOH and oxidant solutions. On the other hand, the opposite trend was observed for the samples etched with the phosphoric acid solution. Whereas the samples etched with the ammonia solution had a scattered
qϕ
B
value, they were not affected by the etching. However, the photoyield increased by 2.5–3.5 times in all kinds of etching. SIPM was found to be sensitive in visualizing the effect of the CL-PEC etching as an image.
We studied the roles of lightly doped carbon in a series of n-GaN Schottky diode epitaxial structures on freestanding GaN substrates, and evaluated the effects of the doping on diode performances. A ...large variation of compensation ratio was observed for carbon doping at (1-2) × 1016 cm−3. A model was proposed to explain this phenomenon, in which a vulnerable balance between donor-type CGa and deep acceptor CN strongly affected the free-carrier generation. Application of Norde plots and reverse biased leakage current in current-voltage measurements suggested provisional optimization for a free-carrier concentration of 8 × 1015 cm−3 to achieve a tradeoff between breakdown voltage and on-resistance of the n-GaN diodes.
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