• Journal of IKEEE
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• v.24 no.4
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• pp.1167-1171
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• 2020

In this work, we proposed a graded gate-doping structure to alleviate an electric field in p-GaN gate layer in order to improve the reliability of normally-off GaN power devices. In a TCAD simulation by Silvaco Atlas, a distribution of the graded p-type doping concentration was optimized to have a threshold voltage and an output current characteristics as same as the reference device with a uniform p-type gate doping. The reduction of an maximum electric field in p-GaN gate layer was observed and it suggests that the gate reliability of p-GaN gate HFETs can be improved.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.29.1-29.1
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• 2009

Fabrication of good quality P-type GaN remained as a challenge for many years which hindered the III-V nitrides from yielding visible light emitting devices. Firstly Amano et al succeeded in obtaining P-type GaN films using Mg doping and post Low Energy Electron Beam Irradiation (LEEBI) treatment. However only few region of the P-GaN was activated by LEEBI treatment. Later Nakamura et al succeeded in producing good quality P-GaN by thermal annealing method in which the as deposited P-GaN samples were annealed in N2 ambient at temperatures above $600^{\circ}C$. The carrier concentration of N type and P-type GaN differs by one order which have a major effect in AlGaN based deep UV-LED fabrication. So increasing the P-type GaN concentration becomes necessary. In this study we have proposed a novel method of activating P-type GaN by electrochemical potentiostatic method. Hydrogen bond in the Mg-H complexes of the P-type GaN is removed by electrochemical reaction using KOH solution as an electrolyte solution. Full structure LED sample grown by MOCVD serves as anode and platinum electrode serves as cathode. Experiments are performed by varying KOH concentration, process time and applied voltage. Secondary Ion Mass Spectroscopy (SIMS) analysis is performed to determine the hydrogen concentration in the P-GaN sample activated by annealing and electrochemical method. Results suggest that the hydrogen concentration is lesser in P-GaN sample activated by electrochemical method than conventional annealing method. The output power of the LED is also enhanced for full structure samples with electrochemical activated P-GaN. Thus we propose an efficient method for P-GaN activation by electrochemical reaction. 30% improvement in light output is obtained by electrochemical activation method.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.331-331
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• 2014

3족 질화물에 기반한 발광다이오드는 비소화물이나 인화물에 비해 여러 가지 장점을 가져 각광받아왔다. 특히, (Al)GaN 에 기반한 자외선 영역 발광 다이오드는 자외선 경화, 소독 등의 여러 가지 응용 가능성을 가진다 [1]. 하지만, 심자외선 영역으로 갈수록 높은 접촉 저항과 투명전극에서의 광흡수에 의해 전류주입 효율과 광추출 효율이 감소하여 결국 외부양자 효율이 더욱 열화되는 특성을 보인다. 이는 넓은 밴드갭을 가지는 물질을 이용하여 p-(Al)GaN 층에서 오믹접촉을 이루어야만 해결이 가능하지만 아직까지 이러한 결과가 보고된 바 없다. 본 연구에서는, 우리는 넓은 밴드갭을 가지는 silicon dioxide (SiO2) 에 전기장을 인가하여 p-GaN, and p-AlGaN 층에 전도성 필라멘트를 형성하여 전기전도도를 부여하는 연구를 진행하였다. p-GaN 과 p-AlGaN 위에서 5 nm 두께의 SiO2는 schottky 한 특성과 280 nm의 파장대역에서 약 97%의 투과율을 보였다. 비록 schottky 장벽이 형성되었지만, 전기전도도가 크게 향상되었으며 심자외선 영역에서 매우 낮은 흡수율을 보였다. 이는 기존의 증착후 열처리를 거쳐 제조된 전극에 비하여 우수한 특성을 지니며 향후 심자외선 영역 발광다이오드의 p-(Al)GaN 층 위에 오믹접촉을 이룰수 있는 가능성을 제시한다.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.3
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• pp.66-74
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• 1999

InAlGaAs/InGaAs HBTs with the various emitter junction gradings(xf=0.0-1.0) and the modified collector structures (collector- I;n-p-n, collector-II;i-p-n) are simulated and analyzed by HMC (Hybrid Monte Carlo) method in order to find an optimum structure for the shortest transit time. A minimum base transit time($ au$b) of 0.21ps was obtainsed for HBT with the grading layer, which is parabolically graded from $x_f$=1.0 and xf=0.5 at the emitter-base interface. The minimum collector transit time($\tau$c) of 0.31ps was found when the collector was modified by inserting p-p-n layers, because p layer makes it possible to relax the electric field in the i-type collector layer, confining the electrons in the $\Gamma$-valley during transporting across the collector. Thus InAlGaAs/InGaAs HBT in combination with the emitter grading($x_f$=0.5) and the modified collector-III showed the transit times of 0.87 psec and the cut-off frequency (f$\tau$) of 183 GHz.

• Advances in nano research
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• v.3 no.1
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• pp.13-27
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• 2015

Size dependent emission properties and the interband optical transition energies in group-III nitride based quantum dots are investigated taking into account the geometrical confinement. Exciton binding energy and the optical transition energy in $Ga_{0.9}In_{0.1}N$/GaN and $Al_{0.395}In_{0.605}N$/AlN quantum dots are studied. The largest intersubband transition energies of electron and heavy hole with the consideration of geometrical confinement are brought out. The interband optical transition energies in the quantum dots are studied. The exciton oscillator strength as a function of dot radius in the quantum dots is computed. The interband optical absorption coefficients in GaInN/GaN and AlInN/AlN quantum dots, for the constant radius, are investigated. The result shows that the largest intersubband energy of 41% (10%) enhancement has been observed when the size of the dot radius is reduced from $50{\AA}$ to $25{\AA}$ of $Ga_{0.9}In_{0.1}N$/GaN ($Al_{0.395}In_{0.605}N$/AlN) quantum dot.

• Electronic Materials Letters
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• v.14 no.6
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• pp.784-792
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• 2018

In this letter, a standard deviation based optimization technique has been applied on High Resolution X-ray Diffraction symmetric and asymmetric scan results to accurately determine the Aluminum molar fraction and lattice relaxation of Molecular Beam Epitaxy grown compositionally graded Aluminum Gallium Nitride (AlGaN)/Aluminum Nitride/Gallium Nitride (GaN) heterostructures. Mathews-Blakeslee critical thickness model has been applied in an alternative way to determine the partially relaxed AlGaN epilayer thicknesses. The coupling coefficient determination has been presented in a different perspective involving sample tilt method by off set between the asymmetric planes of GaN and AlGaN. Sample tilt is further increased to determine mosaic tilt ranging between $0.01^{\circ}$ and $0.1^{\circ}$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.6
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• pp.282-288
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• 2017

In this paper, GaAs/AlGaAs multi-layer structure was grown by liquid phase epitaxy with graphite sliding boat, which can be used as a device structure of a photocathode image sensor. The multi-layer structure was grown on an n-type GaAs substrate in the sequence as follows: GaAs buffer layer, Zn-doped p-type AlGaAs layer as etching stop layer, Zn-doped p-type GaAs layer, and Zn-doped p-type AlGaAs layer. The Characteristics of GaAs/AlGaAs structures were analyzed by using scanning electron microscope (SEM), secondary ion mass spectrometer (SIMS) and hall measurement. The SEM images shows that the p-AlGaAs/p-GaAs/p-AlGaAs multi-layer structure was grown with a mirror-like surface on a whole ($1.25mm{\times}25mm$) substrate. The Al composition in the AlGaAs layer was approximately 80 %. Also, it was confirmed that the free carrier concentration in the p-GaAs layer can be adjusted to the range of $8{\times}10^{18}/cm^2$ by hall measurement. In the result, it is expected that the p-AlGaAs/p-GaAs/p-AlGaAs multi-layer structure grown by the LPE can be used as a device structure of a photoelectric cathode image sensor.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.655-660
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• 2001

Surface photovoltage spectroscopy was used to study $In_{0.5}(Ga_{1-x}Al_x)_{0.5}P/GaAs$ grown by metalorganic chemical vapor deposition(MOCVD). Energy gap related transition in GaAs and $In_{0.5}(Ga_{1-x}Al_x)_{0.5}P$ were observed. By measuring the frequency dependence of $In_{0.5}(Ga_{1-x}Al_x)_{0.5}P/GaAs$, we observed that SPV line shape does not chance, whereas the amplitude change. This results is due to the difference in the lifetimes of the photocarriers in GaAs and in $In_{0.5}(Ga_{1-x}Al_x)_{0.5}P$. We also have evaluated the parameters that describe the temperature dependences of the band gap.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.667-671
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• 1998

The photoluminescence (pL) characteristics of hydride vapor phase epiyaxy (HVPE) grown GaN films on $MgAl_{2}O_{4}$ substrate were investigated with several growth conditions. The GaN films on $MgAl_{2}O_{4}$ substrate is autodoped with Mg atoms which thermally out-diffused from substrate lead to a PL characteristics of impurity doped ones. The Mg-related emission band intensity decreased with growth temperature may due to the evaporation of Mg atoms at the GaN film surfaces. and it also decreased with GaN film thicknesses. We can estimate the diffusion coefficient of Mg atoms in GaN under the consideration of diffusion phenomena between two infinite solids lead to a value of D= 2$\times$$lO^{-10}\textrm{cm}^2/sec.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.1
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• pp.1-6
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• 2020

In this research, 50 nm thick AlN thin films were deposited on the patterned sapphire (0001) substrate by using HVPE (Hydride Vapor Phase Epitaxy) system and then epitaxial layer structure was grown by MOCVD (metal organic chemical vapor deposition). The surface morphology of the AlN buffer layer film was observed by SEM (scanning electron microscopy) and AFM (atomic force microscope), and then the crystal structure of GaN films of the epitaxial layer structure was investigated by HR-XRC (high resolution X-ray rocking curve). The XRD peak intensity of GaN thin film of epitaxial layer structure deposited on AlN buffer layer film and sapphire substrate was rather higher in case of that on PSS than normal sapphire substrate. In AFM surface image, the epitaxial layer structure formed on AlN buffer layer showed rather low pit density and less defect density. In the optical output power, the epitaxial layer structure formed on AlN buffer layer showed very high intensity compared to that of the epitaxial layer structure without AlN thin film.