• JSTS:Journal of Semiconductor Technology and Science
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• v.2 no.2
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• pp.93-101
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• 2002

We have proposed and fabricated two lateral type field emission diodes, poly-Si emitter by utilizing the local oxidation of silicon (LOCOS) and GaN emitter using metal organic chemical vapor deposition (MOCVD) process. The fabricated poly-Si diode exhibited excellent electrical characteristics such as a very low turn-on voltage of 2 V and a high emission current of $300{\;}\bu\textrm{A}/tip$ at the anode-to-cathode voltage of 25 V. These superior field emission characteristics was speculated as a result of strong surface modification inducing a quasi-negative electron affinity and the increase of emitting sites due to local sharp protrusions by an appropriate activation treatment. In respect, two kinds of procedures were proposed for the fabrication of the lateral type GaN emitter: a selective etching method with electron cyclotron resonance-reactive ion etching (ECR-RIE) or a simple selective growth by utilizing $Si_3N_4$ film as a masking layer. The fabricated device using the ECR-RIE exhibited electrical characteristics such as a turn-on voltage of 35 V for $7\bu\textrm{m}$ gap and an emission current of~580 nA/l0tips at anode-to-cathode voltage of 100 V. These new field emission characteristics of GaN tips are believed to be due to a low electron affinity as well as the shorter inter-electrode distance. Compared to lateral type GaN field emission diode using ECR-RIE, re-grown GaN emitters shows sharper shape tips and shorter inter-electrode distance.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.9
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• pp.104-113
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• 1994

We have fabricated n-p-n HBTs using 3-inchAlgaAs/GaAs hetero structure epi-wafers grown by MBE. DC and AC characteristics of HBT devices were measured and analyzed. For HBT epi-structure, Al composition of emitter was graded in the region between emitter cap and emitter. And base layer was designed with concentration of 1${\times}10^{19}/cm^{3}$ and thickness of 50nm, and Be was used as the p-type dopant. Principal processes for device fabrication consist of photolithography using i-line stepper, wet mesa etching, and lift-off of each ohmic metal. The PECVD SiN film was used as the inslator for the metal interconnection. HBT device with emitter size of 3${\times}10{\mu}m^{2}$ resulted in cut-off frequency of 35GHz, maximum oscillation frequency of 21GHz, and current gain of 60. The distribution of the ideality factor of collector and base current was very uniform, and the average values of off-set voltage and current was very uniform, and the average values of off-set voltage and current gain were 0.32V and 32 within a 3-inch wafer.

• Proceedings of the IEEK Conference
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• 2001.06b
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• pp.213-216
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• 2001

The use of a thin film of indium between the ITO and the $n^{+}$-InP contact layers for InP/InGaAs HPTs was studied without degrading its excellent optical transmittance properties. ITO/$n^{+}$-InP ohmic contact was successfully achieved by the deposition of Indium and thermal annealing. The specific contact resistance of about 6.6$\times$$10^{-4}$$\Omega\textrm{cm}^2$ was measured by use of the transmission line method (TLM). However, as the thermal annealing was just performed to ITO/$n^{+}$-InP contact without the deposition of Indium between ITO and $n^{+}$-InP, it exhibited schottky characteristics. In the applications, the DC characteristics of InP/InGaAs HPTs with ITO emitter contacts was compared with that of InP/InGaAs HBTs with the opaque emitter contacts.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.236-236
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• 2010

단일접합 $n^+-p/p^+$ (p-emitter) 및 $p^+-n/n^+$ (n-emitter) GaAs 태양전지 (Solar Cell)를 각각 제작하여, 그 소자특성을 비교 분석하였다. AM 1.5 (1 sun, $100\;mW/cm^2$) 표준광을 조사할 경우, p-emitter/n-emitter 소자의 개방회로전압 (Voc), 단락회로전류 (Jsc), 충전율 (FF), 효율 (Eff)은 각각 0.910/0.917 V, $15.9/16.1\;mA/cm^2$, 78.7/78.9, 11.4/12.1%로서, n-emitter 소자가 다소 크지만 거의 비슷한 값을 가지고 있었다. 태양전지의 집광 특성을 분석하기 위하여 조사광의 출력에 따른 태양전지의 소자 특성을 측정하였다. 조사광 강도가 높아짐에 따라 p-emitter 소자의 특성은 점진적으로 증가하는 반면, n-emitter는 1.3 sun에서 약 1.4 배의 최대 효율 (17%)을 나타내고 조사광이 더 증가함에 따라 급격히 감소하는 특성을 보여 주었다. (그림 참고) 본 연구에서 사용한 2종류 소자의 층구조는 서로 반대되는 대칭구조로서, 모두 가까이에 위치하고 있는 표면전극 (surface finger) 방향으로 소수전하 (minority carrier)가 이동하고 다수전하 (majority carrier)는 기판 (두께 $350\;{\mu}m$)을 통한 먼 거리의 후면전극 (back electrode)으로 표류 (drift)되도록 설계되어 있다. 이때, n-emitter에서는 이동도 (mobility)와 확산길이 (diffusion length)가 높은 전자가 후면전극으로 이동하기 때문에 적정밀도의 전자-정공 쌍 (EHP)이 여기될 경우에는 Jsc와 Eff가 극대화되지만, 조사광 강도 또는 EHP가 더 높아질 경우에는 직렬저항의 증가와 함께 전류-전압 (I-V)의 이상인자 (ideality factor)가 커짐으로서 FF와 효율이 급격히 감소한 결과로 분석된다. 현재 전산모사를 통한 자세한 분석을 진행하고 있으며, 본 결과는 효율 극대화를 위한 최적 층구조 및 도핑 밀도 설계에 활용할 수 있을 것으로 판단된다.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.1
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• pp.30-39
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• 1991

The influence of physical parameters (Al mole fraction, thickness, doping concentration) in the window and emitter on the efficiency characteristics of heteroface p-$Al_{x}Ga_{1-x}As/p-GaAs/n-GaAs/n^{+}$-GaAs solar cell is investigated. The maximum efficiency theoretically calculated in this device is obtained when a thickness of the window is in a range of (400-1000))$\AA$and a thickness/doping concentration of the emitter is in a range of (0.5-0.8)$\mu$m/(1-7)${\times}10^{17}cm^{-3}$, respectively. Also is the efficiency improved according to the increase of Al mole fraction in the indirect gap window(0.41${\le}x{\le}1.0$). The optimum designed heteroface cell with an area of 0.165cm$^2$fabricated using MOCVD exhibits an active area conversion efficiency of 17%, having a short circuit current density of 21.2mA/cm\ulcorner an open circuit voltage of 0.94V, and a fill factor of 0.75 under ELH-100mW/cm$^2$illumination.

• 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.

• Proceedings of the IEEK Conference
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• 2000.11b
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• pp.229-232
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• 2000

InP/lnGaAs HPT's were fabricated by employing Indium Tin Oxide(ITO) transparent emitter contact. The device showed the current gaing 70 was obtained but the emitter series resistance was significantly increased. the electrical charateristics of the device were similar to HBT's. However Vceoff was shifted the positive direction. Such a shift ma be resulted from the formation of the shottky barrier rather than the ohmic contact between ITO and n+ InP emitter.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.184-184
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• 2012

Recently, InGaN/GaN multi-quantum well grown on GaN pyramid structures have attracted much attention due to their hybrid characteristics of quantum well, quantum wire, and quantum dot. This gives us broad band emission which will be useful for phosphor-free white light emitting diode. On the other hand, by using quantum dot emission on top of the pyramid, site selective single photon source could be realized. However, these structures still have several limitations for the single photon source. For instance, the quantum efficiency of quantum dot emission should be improved further. As detection systems have limited numerical aperture, collection efficiency is also important issue. It has been known that micro-cavities can be utilized to modify the radiative decay rate and to control the radiation pattern of quantum dot. Researchers have also been interested in nano-cavities using localized surface plasmon. Although the plasmonic cavities have small quality factor due to high loss of metal, it could have small mode volume because plasmonic wavelength is much smaller than the wavelength in the dielectric cavities. In this work, we used localized surface plasmon to improve efficiency of InGaN qunatum dot as a single photon emitter. We could easily get the localized surface plasmon mode after deposit the metal thin film because lnGaN/GaN multi quantum well has the pyramidal geometry. With numerical simulation (i.e., Finite Difference Time Domain method), we observed highly enhanced decay rate and modified radiation pattern. To confirm these localized surface plasmon effect experimentally, we deposited metal thin films on InGaN/GaN pyramid structures using e-beam deposition. Then, photoluminescence and time-resolved photoluminescence were carried out to measure the improvement of radiative decay rate (Purcell factor). By carrying out cathodoluminescence (CL) experiments, spatial-resolved CL images could also be obtained. As we mentioned before, collection efficiency is also important issue to make an efficient single photon emitter. To confirm the radiation pattern of quantum dot, Fourier optics system was used to capture the angular property of emission. We believe that highly focused localized surface plasmon around site-selective InGaN quantum dot could be a feasible single photon emitter.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.281-281
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• 2014

The field emission properties of GaN are reported in the present study. To be a good field emitter, it requires a low work function, high aspect ratio, and strong mechanical stability. In the case of GaN, it has a quite low work function (4.1eV) and strong chemical/mechanical/thermal stabilities. However, so far, it was difficult to fabricate vertical GaN nanostructures with a high aspect ratio. In this study, we successfully achieved vertically well aligned GaN nanostructures with chemical vapor-phase etching methods [1] (Fig. 1). In this method, we chemically etched the GaN film using hydrogen chloride and ammonia gases at high temperature around $900^{\circ}C$. This process effectively forms vertical nanostructures without patterning procedure. This favorable shape of GaN nanostructures for electron emitting results in excellent field emission properties such as a low turn-on field and long term stability. In addition, we observed a uniform fluorescence image from a phosphor film attached at the anode part. The turn-on field for the GaN nanostructures is found to be about $0.8V/{\mu}m$ at current density of $20{\mu}A$/cm^2. This value is even lower than that of typical carbon nanotubes ($1V/{\mu}m$). Moreover, threshold field is $1.8V/{\mu}m$ at current density of $1mA$/cm^2. The GaN nanostructures achieved a high current density within a small applied field range. We believe that our chemically etched vertical nanostructures are the promising structures for various field emitting devices.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.11
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• pp.546-550
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• 2002

In this paper, Heterojunction phototransistors(HPT's) with an optically transparent ITO emitter contacts were fabricated. The ITO ohmic contacts were realized by employing thin imdium layer between the ITO and $n^+$-InP layers. The ITO contact was annealed at $250^{\circ}C$. The specific contact resistance of about $6.6{\times}10^{-4}{\Omega}cm^2$ was measured by use of the transmission line model (TLM). Heterojunction bipolar transistors (HBTs) having the same device layout were fabricated to compare with HPTs. The DC characteristics of the InP/InGaAs HPT showed the similar electrical characteristics of the HBT. Emitter contact resistance($R_E$) of about $6.4{\Omega}$ was extracted, which was very similar to that of the HBT. The optical characteristics of HPT's were generated by illuminating the device with light from $1.3{\mu}m$ light. It showed that HPT's can be controlled optically.