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ABSTRACT: AlGaN/GaN heterostructure Schottky barrier pho-todetector (PD) with multi-Mg x N y /GaN buffer was proposed and fabricated. Compared with AlGaN/GaN heterostructure PD prepared on conventional low-temperature GaN buffer, it was found that we can reduce dark leakage current by more than three orders of magnitude. It was also found that we can use the multi-Mg x N y /GaN buffer to suppress photoconductance gain, enhance UV-to-visible rejection ratio, reduce noise level and enhance the detectivity. Index Terms—AlGaN/GaN heterostructure, multi-Mg x N y /GaN buffer, Schottky barrier photodetector.
IEEE Sensors Journal ; 9. · 1.52 Impact Factor
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ABSTRACT: AlGaN/GaN heterostructure Schottky barrier pho-todetector (PD) with multi-Mg x N y /GaN buffer was proposed and fabricated. Compared with AlGaN/GaN heterostructure PD prepared on conventional low-temperature GaN buffer, it was found that we can reduce dark leakage current by more than three orders of magnitude. It was also found that we can use the multi-Mg x N y /GaN buffer to suppress photoconductance gain, enhance UV-to-visible rejection ratio, reduce noise level and enhance the detectivity. Index Terms—AlGaN/GaN heterostructure, multi-Mg x N y /GaN buffer, Schottky barrier photodetector.
IEEE Sensors Journal ; 9. · 1.52 Impact Factor
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ABSTRACT: Nitride-based ultraviolet (UV) photosensors with a low-temperature (LT) AlGaN interlayer were fabricated and characterized.
Material analysis results showed that dark pits corresponding to threading dislocation (TD) terminations were almost invisible
after inserting the LT AlGaN interlayer. It was also found that we could significantly suppress the dark leakage current by
using the LT AlGaN interlayer owing to TD annihilation and demultiplication processes. For photosensors with the LT AlGaN
interlayer, the responsivity at 360nm and UV-to-visible rejection ratio were found to be 0.12A/W and 2.45×103, respectively, under 5V applied bias.
Journal of Electronic Materials 04/2012; 39(1):29-33. · 1.47 Impact Factor
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ABSTRACT: We report the fabrication of GaN photodetectors (PDs) prepared on nanorod template. Using the nanorods template, it was found that we can effectively suppress leakage current, ultraviolet-to-visible rejection ratio and photoconductive gain of the PDs. With -2 V applied bias, it was found that noise equivalent power (NEP) and normalized detectivity (D*) were 7.00 × 10<sup>-10</sup> W and 2.26 × 10<sup>9</sup> cmHz<sup>0.5</sup> W<sup>-1</sup>, respectively, for the PD prepared on nanorods template. With the same -2 V bias, it was found that NEP and D* were 3.56 × 10<sup>-6</sup> W and 4.44 × 10<sup>5</sup> cmHz<sup>0.5</sup> W<sup>-1</sup>, respectively, for the PD prepared on a conventional sapphire substrate.
IEEE Sensors Journal 11/2010; · 1.52 Impact Factor
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ABSTRACT: The authors report the fabrication of GaN-based metal-semiconductor-metal photodetectors (PDs) on a conventional flat sapphire substrate and on a nanorod template. Compared with the PD prepared on the flat sapphire substrate, it was found that leakage current of the PD prepared on the nanorod template was significantly smaller due to the improved crystal quality. It was also found that we can reduce the photoconductive gain and enhance ultraviolet-to-visible rejection ratio by using the nanorod template.
IEEE Photonics Technology Letters 06/2010; · 2.19 Impact Factor
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ABSTRACT: We report an AlGaN/GaN high electron mobility transistors (HEMTs) based on InGaN/GaN multiquantum-well (MQW) structure. When InGaN/GaN MQW structure was inserted, InGaN layer has an opposite piezoelectric polarization field compared to AlGaN, which results in a very sharp rise of the conduction band. The raised potential barrier can help to improve carrier confinement and obtain a larger main peak transconductance of 111 mS/mm and satellite peak transconductance of 24 mS/mm, corresponding to AlGaN/GaN heterojunction and InGaN layer. MQW-based metal-oxide-semiconductor-HEMT was also fabricated and significantly reduced the leakage current and increased transconductance as a result of passivation by Ta2O5 gate oxide.
Applied Physics Letters 05/2010; 96(21):212105-212105-3. · 3.84 Impact Factor
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ABSTRACT: III-nitride Schottky rectifiers (SRs) with (i.e., SR_A) and without (i.e., SR_B) the AlGaN/GaN/AlGaN/GaN quadruple layer were both fabricated. It was found that we could achieve a lower leakage current from SR_A. Under reverse bias, it was found that SR_A showed a more than five orders magnitude smaller dark current than that in SR_B. It was also found that lower on-state resistance was due to the larger Schottky barrier height and larger breakdown voltage was due to reduced defect densities in SR_A. The SRs with a quadruple layer was suitable for applications to low noise or/and ultraviolet (UV) detection as well.
IEEE Sensors Journal 05/2010; · 1.52 Impact Factor
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ABSTRACT: In this study, AlGaN/GaN two-dimensional electron gas (2DEG) heterostructures were grown by metal organic chemical vapor deposition (MOCVD). It was found that we could reduce reverse leakage current and provide high-voltage operation by introducing multiple MgxNy/GaN layers into the conventional Schottky barrier photodiodes (SBPD). An atomic force microscopy (AFM) scan image showed that surface pits of TD terminations were hardly observed as the multiple MgxNy/GaN layers were grown before subsequently depositing a high-temperature (HT) AlGaN/GaN epitaxial layer. A larger Schottky barrier height (ΦB) and smaller ideality factor (n) extracted from the current–voltage (I–V) curve for SBPD with multiple MgxNy/GaN layers also suggested that better crystal quality and rectifying properties were achieved. The larger value of ΦB might be explained by the reduction of the TD density and interface state (IS) density.
Semiconductor Science and Technology 09/2009; 24(10):105005. · 1.72 Impact Factor
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ABSTRACT: We present the characteristics of an AlGaN/GaN Schottky barrier ultraviolet (UV) photodetectors (PDs) with and without a GaN sandwich layer. The effect of inserting this secondary GaN buffer layer on the growth mode and crystal properties of the whole epitaxial GaN layer was reported. It was found that we could reduce defect density and thus improve crystal quality of the AlGaN/GaN Schottky barrier UV PDs by using a GaN sandwich layer. It was also found that we could use the GaN sandwich structure to suppress photoconductive gain (PCG), enhance UV-to-visible rejection ratio (UTV-RR), reduce noise level, and enhance the detectivity of the fabricated PDs.
IEEE Sensors Journal 08/2009; · 1.52 Impact Factor
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ABSTRACT: AlGaN/GaN metal-semiconductor-metal photodetectors (MSM PDs) with a low-temperature (LT) AlGaN interlayer (IL) were fabricated. Compared with the conventional AlGaN/GaN MSM PD, it was found that leakage current can be suppressed by insertion of a LT AlGaN IL due to the reduction of surface pits and improvement of crystalline quality. It was also found that larger photoresponsivity can be achieved due to the enhanced electric field strength as a result of inserting a LT AlGaN IL. Furthermore, suppressed photoconductive gain, lower noise level, and larger detectivity of MSM PD can also be achieved by using a LT AlGaN IL.
IEEE Sensors Journal 07/2009; · 1.52 Impact Factor
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ABSTRACT: AlGaN/GaN heterostructure Schottky barrier photodetector (PD) with multi-Mg<sub>x</sub>N<sub>y</sub>/GaN buffer was proposed and fabricated. Compared with AlGaN/GaN heterostructure PD prepared on conventional low-temperature GaN buffer, it was found that we can reduce dark leakage current by more than three orders of magnitude. It was also found that we can use the multi-Mg<sub>x</sub>N<sub>y</sub>/GaN buffer to suppress photoconductance gain, enhance UV-to-visible rejection ratio, reduce noise level and enhance the detectivity.
IEEE Sensors Journal 03/2009; · 1.52 Impact Factor
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ABSTRACT: GaN-based ultraviolet (UV) photodetectors (PDs) separately prepared with a conventional single low-temperature (LT) GaN buffer layer and a 12-pair Mg<sub>x</sub>N<sub>y</sub>-GaN buffer layer were both fabricated. It was found that we could reduce threading dislocation (TD) density and thus improve crystal quality of the GaN-based UV PDs by using the 12-pair Mg<sub>x</sub>N<sub>y</sub>-GaN buffer layer. With a -2-V applied bias, it was found that the reverse leakage currents measured from PDs with a single LT GaN buffer layer and that with a 12-pair Mg<sub>x</sub>N<sub>y</sub>-GaN buffer layer were 4.57 times 10<sup>-6</sup> and 1.44 times 10<sup>-12</sup> A, respectively. It was also found that we could use the 12-pair Mg<sub>x</sub>N<sub>y</sub>-GaN buffer layer to suppress photoconductive gain, enhance UV-to-visible rejection ratio, reduce noise level, and enhance the detectivity.
IEEE Journal of Quantum Electronics 11/2008; · 1.88 Impact Factor
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ABSTRACT: We present the characteristics of a nitride-based UV metal–semiconductor–metal photodetector (MSM PD) with an in situ low-temperature
(LT) grown AlN cap layer. From atomic-force microscopy scan images, we could clearly see that surface pits on the sample surface
are almost invisible with an LT AlN cap layer but can be observed in a conventional cap layer. Compared with conventional
MSM PDs, it was found that we achieved smaller dark current and larger UV-to-visible rejection ratio for the PDs with an LT
AlN cap layer. With a
applied bias, the UV-to-visible rejection ratio between 360 and
was
for the MSM PDs with an LT AlN cap layer. The calculated noise equivalent power and normalized detectivity biased at
for the MSM PDs with an LT AlN cap layer was
and
, respectively.
Journal of The Electrochemical Society. 09/2008; 155(10):J287-J289.
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ABSTRACT: Schottky barrier diodes (SBDs) with multi-
buffer were fabricated and investigated. It was found that we can effectively suppress the formation of threading dislocation
in the epitaxial layers and thus obtain better crystal quality using the multi-
buffer. It was also found that we can achieve a larger effective Schottky barrier height and thus reduce leakage current
of the SBDs by using the multi-
buffer.
Journal of The Electrochemical Society. 09/2008; 155(10):H716-H719.
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ABSTRACT: We report the fabrication of GaN-based Schottky barrier diodes with multi-MgxNy/GaN buffer. Compared to conventional devices with a low-temperature GaN buffer, we achieved a six orders of magnitude smaller leakage current. It was also found that effective Schottky barrier height is larger for the proposed device due to the reduction in surface defect density by using the multi-MgxNy/GaN buffer.
Applied Physics Letters 09/2008; 93(13):132110-132110-3. · 3.84 Impact Factor
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ABSTRACT: GaN UV metal–semiconductor–metal photodetectors (MSM PDs) with an unactivated Mg-doped cap layer and sputtered indium tin
oxide (ITO) were fabricated. Compared with conventional MSM PDs without a cap layer, it was found that we could achieve a
significantly much smaller dark current, larger UV to visible rejection ratio, and larger normalized detectivity by inserting
an unactivated Mg-doped GaN cap layer. The dark leakage current for the MSM PDs with an unactivated Mg-doped GaN cap layer
was shown to be about ten orders of magnitude smaller than that for the conventional MSM PDs. Under a 0.5 V bias, the measured
responsivity and UV-to-visible rejection ratio were 0.017 A/W and
, respectively, for the MSM PDs with an unactivated Mg-doped GaN cap layer. This result could be attributed to the thicker
and higher potential barrier and effective surface passivation after inserting this in situ grown cap layer. With a 1 V applied
bias, it was also found that we could achieve a lower noise level and a higher normalized detectivity of
by inserting an unactivated Mg-doped GaN cap layer into MSM PDs.
Journal of The Electrochemical Society. 05/2008; 155(6):J165-J167.
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ABSTRACT: GaN-based ultraviolet (UV) photodetectors (PDs) separately prepared with a conventional single low-temperature (LT) GaN buffer layer and a 12-pair Mg x N y –GaN buffer layer were both fabricated. It was found that we could reduce threading dislocation (TD) density and thus improve crystal quality of the GaN-based UV PDs by using the 12-pair Mg x N y –GaN buffer layer. With a 2-V applied bias, it was found that the reverse leakage currents measured from PDs with a single LT GaN buffer layer and that with a 12-pair Mg x N y –GaN buffer layer were 4 57 10 6 and 1 44 10 12 A, respectively. It was also found that we could use the 12-pair Mg x N y –GaN buffer layer to suppress photoconductive gain, enhance UV-to-visible rejection ratio, reduce noise level, and enhance the detectivity. Index Terms—Multiple Mg x N y –GaN buffer layers, photode-tector (PD), ultraviolet (UV).
IEEE JOURNAL OF QUANTUM ELECTRONICS. 01/2008; 44.
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ABSTRACT: GaN-based ultraviolet photodiodes with a semi-insulating Mg-doped GaN cap layer were fabricated and characterized. Dark leakage current of the aforementioned photodiodes was much smaller than that of the conventional ones without the Mg-doped GaN cap layer due to a thicker and higher potential barrier and less amounts of interface states after inserting the Mg-doped GaN cap layer. The ultraviolet to visible rejection ratio is 3.44 x 10<sup>3</sup> by inserting a semi-insulating Mg-doped GaN cap layer with a -IV applied bias. In this study, we also discuss the noise characteristics. It was found that minimum noise equivalent power and maximum detectivity of our photodiode were 1.2 x 10<sup>-12</sup> W and 9.34 x 10<sup>11</sup> cmHz<sup>0.5</sup> W<sup>-1</sup>, respectively.
IEEE Sensors Journal 10/2007; · 1.52 Impact Factor
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ABSTRACT: Here, we present the characteristics of a novel GaN- based ultraviolet (UV) photodiode (PD) with a low-temperature (LT) AIN cap layer. The dark leakage current for the PD with the LT-AIN cap layer was shown to be about four orders of magnitude smaller than that for the conventional PDs. It was found that we could achieve larger UV to visible rejection ratio by inserting an LT-AIN cap layer. It was also found that we could improve minimum noise equivalent power and maximum normalized detectivity of the PD by inserting an LT-AIN cap layer.
IEEE Sensors Journal 10/2007; · 1.52 Impact Factor
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ABSTRACT: InGaN-GaN multiple-quantum-well metal-semiconductor-metal photodiodes (PDs) with in situ grown 40-nm-thick unactivated semi-insulating Mg-doped GaN cap layer were successfully fabricated. The dark leakage current of this PD was comparably much smaller than that of conventional PD without the semi-insulating layer, because of a thicker and higher potential barrier of semi-insulating cap layer, and also a smaller number of surface states involved. For the PDs with the semi-insulating Mg-doped GaN cap layers, the responsivity at 380nm was 0.372A/W when biasing at 5 V. In short, incorporating a semi-insulating Mg-doped GaN cap layer into the PDs beneficially leads to the suppression of dark current and a corresponding improvement in the ultraviolet-to-visible rejection ratio
IEEE Photonics Technology Letters 07/2007; · 2.19 Impact Factor
