원자층 증착법을 이용한 AlN 박막을 통한 AlGaN/GaN 이종접합의 전류 개선 연구

장원호,김태현,임준혁,차호영 대한전자공학회 2021 전자공학회논문지 Vol.58 No.5

본 연구에서는 얇은 AlGaN 장벽층을 갖는 AlGaN/GaN 이종접합 소자의 특성 향상을 위하여 원자층 증착법 방식을 이용한 AlN 박막을 적용한 결과에 관하여 연구하였다. 얇은 AlGaN/GaN 층 위의 AlN 박막 증착은 분극 효과를 향상시키며 이를 통해 계면의 이차원 전자가스 (2-dimensional electron gas, 2DEG) 농도가 증가하며 전류 특성 향상이 가능하다. 본 실험에서는 4nm의 얇은 AlGaN 장벽층을 갖는 AlGaN/GaN 이종접합 구조에 10nm 두께의 AlN 박막을 적용하였으며 이때 2DEG의 전자 농도가 급격하게 증가하는 것을 확인하였고 증가된 전자 농도는 통상적으로 사용되는 20nm 정도의 두꺼운 AlGaN 장벽층을 갖는 구조의 특성과 유사함을 확인하였다. 또한, AlN 박막과 함께 추가적인 SiNx 박막 패시베이션을 증착하였을 때 더욱 큰 2DEG의 전자 농도 및 전류량 증가를 확인하였다. 해당 연구 결과를 통해 AlGaN/GaN 이종접합 구조의 2DEG 특성을 원자층 증착법 방식을 이용한 박막 공정으로 획기적으로 향상 시킬 수 있음을 확인하였다. The effects of an AlN film grown by atomic layer deposition on the thin AlGaN barrier AlGaN/GaN heterojunction structure were investigated. The AlN thin film induced stronger polarization effects on thin-AlGaN/GaN structure, which increased a 2-dimensional electron gas (2DEG) density. Using a 10 nm ALD AlN thin film on 4 nm of thin AlGaN/GaN epistructure, the 2DEG carrier density was drastically enhanced, which is comparable to a conventional 20 nm thick AlGaN structure. Further enhancement of 2DEG carrier density and current level was achieved after SiNx passivation was added on AlN film. In this study, the 2DEG characteristics of the AlGaN/GaN heterojunction structure can be dramatically improved by the atomic layer deposition method was confirmed.

1/<i>f</i> noise characteristics of AlGaN/GaN HEMTs with periodically carbon-doped GaN buffer layer

Im, Ki-Sik,Choi, Jinseok,Hwang, Youngmin,An, Sung Jin,Roh, Jea-Seung,Kang, Seung-Hyeon,Lee, Jun-Hyeok,Lee, Jung-Hee Elsevier 2019 MICROELECTRONIC ENGINEERING Vol.215 No.-

<P><B>Abstract</B></P> <P>We investigate the DC and 1/<I>f</I> noise properties in Al<SUB>0.25</SUB>Ga<SUB>0.75</SUB>N/GaN high-electron mobility transistors (HEMTs) with two types of 2 μm-thick periodically carbon-doped GaN buffer layer (PC-doped GaN buffer) with and without inserting the 30 nm-thick Al<SUB>0.05</SUB>Ga<SUB>0.95</SUB>N back barrier layer between the GaN channel layer and the PC-doped GaN buffer. The PC-doped GaN buffer layer consists of multiple layers of 12 nm-thick C-doped GaN layer with doping concentration of 1 × 10<SUP>18</SUP> cm<SUP>−3</SUP> and 50 nm-thick undoped GaN layer with unintentional n-typing concentration of 2 × 10<SUP>16</SUP> cm<SUP>−3</SUP>. A reference AlGaN/GaN HEMT with 2 μm-thick highly-resistive GaN buffer layer without C-doping is also fabricated for comparison. Similarly to the reference AlGaN/GaN HEMT, the AlGaN/GaN HEMTs with PC-doped GaN buffer show typical 1/<I>f</I> noise characteristics mainly due to the trapping effects at the AlGaN/GaN interface from subthreshold region to strong-accumulation region, which indicates that the deep trapping effects in the PC-doped GaN buffer layer is negligible, and experience the correlated mobility fluctuations (CMF), which is convinced from the drain current power spectral density (PSD) versus drain current. At off-state (deep-subthreshold region), on the other hand, the HEMTs with the PC-doped GaN buffer layer exhibit 1/<I>f</I> <SUP>2</SUP> noise characteristics, which are closely related to the generation-recombination (g-r) noise caused by the spatial trapping/detrapping process between the deep acceptor in the C-doped layer and the shallow donor in the undoped layer in the PC-doped GaN buffer, while the reference HEMT still shows typical 1/<I>f</I> noise characteristics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Noise characteristics in AlGaN/GaN HEMTs with/without PC-doped buffer layer were investigated. </LI> <LI> PC-doped buffer layer consists of 12 nm-thick carbon-doped GaN and 50 nm-thick un-doped GaN. </LI> <LI> All devices exhibited 1/<I>f</I> noise properties and CMFs from subthreshold to strong-accumulation. </LI> <LI> At off-state, PC-doped buffer devices exhibited 1/<I>f</I> <SUP>2</SUP> noise properties at frequency > 40 Hz. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

혼합소스 수소화물기상 성장법에 의한 수직 구조 발광 다이오드의 에피층 특성

김경화,이강석,안형수,전인준,조채룡,이상칠,김석환 한국물리학회 2020 New Physics: Sae Mulli Vol.70 No.4

기판이 제거된 수직 구조 청색 발광 다이오드 제작을 위하여 혼합소스 수소화물기상 성장법 (HVPE) 으로 두꺼운 Si-doped GaN (GaN:Si) 층과 AlGaN/GaN 이중-이종구조 (DH)를 포함하는 에피층을 성장하였다. 두꺼운 GaN:Si 층이 에피층에 존재하는 관통 어긋나기 (TD)의 영향을 최소화하기 위해 덩어리(bulk) 처럼 성장 시켰다. AlGaN/GaN 이중-이종구조는 두꺼운 GaN:Si 층 위에 연속적으로 성장되었으며, AlGaN/GaN 이중-이종구조와 GaN:Si 층 내의 TD 밀도는 전계방출 주사 전자 현미경 (FESEM) 과투과 전자 현미경 (TEM)으로 조사하였다. 그 결과 혼합소스 수소화물기상 성장법으로 기존의 사파이어기판에 성장한 에피층과 비교하여 관통 어긋나기 밀도를 감소시키는 역할의 두꺼운 GaN:Si 에피층을성장하여 수직 구조 발광 다이오드를 제작하는데 성공하였다. In the preparation of a vertical blue light-emitting diode (LED) whose conventional substrate had been removed, a previously developed method based on mixed-source hydride vapor phase epitaxy (HVPE) was used to grow the epilayers, including a thick Si-doped GaN (GaN:Si) layer and an AlGaN/GaN double-heterostructure (DH). The thick GaN:Si layer was grown like a bulk material to minimize the effect of threading dislocations (TDs) formed during the epilayer growth. The AlGaN/GaN DH was then grown on the GaN:Si layer, and the dislocation density in both the AlGaN/GaN DH and the GaN:Si layer was investigated by using field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Furthermore, by using the thick GaN:Si epilayer like a bulk material as both a buffer layer and a new substrate for the vertical LED, we succeeded in fabricating a vertical blue LED by using mixed-source HVPE.

Investigating gate metal induced reduction of surface donor density in GaN/AlGaN/GaN heterostructure by electroreflectance spectroscopy

신종훈,김광중,김규상 한국물리학회 2015 Current Applied Physics Vol.15 No.11

The internal field of GaN/AlGaN/GaN heterostructure on Si-substrate was investigated by varying the thickness of an undoped-GaN capping layer using electroreflectance spectroscopy. The four samples investigated are AlGaN/GaN heterostructure without a GaN cap layer (reference sample) and three other samples with GaN/AlGaN/GaN heterostructures in which the different thickness of GaN cap layer (2.7 nm, 7.5 nm, and 12.4 nm) has been considered. The sheet carrier density (ns) of a two-dimensional electron gas has decreased significantly from 4.66 × 1012 cm-2 to 2.15 × 1012 cm-2 upon deposition of a GaN capping layer (12.4 nm) over the reference structure. Through the analysis of internal fields in each GaN capping and AlGaN barrier layers, it has been concluded that the undiminished surface donor states (ns) of a reference structure and the reduced ns caused by the Au gate metal are approximately 5.66 × 1012 cm-2 and 1.08 × 1012 cm-2, respectively.

Investigating gate metal induced reduction of surface donor density in GaN/AlGaN/GaN heterostructure by electroreflectance spectroscopy

Shin, J.H.,Kim, K.C.,Kim, K.S. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.11

The internal field of GaN/AlGaN/GaN heterostructure on Si-substrate was investigated by varying the thickness of an undoped-GaN capping layer using electroreflectance spectroscopy. The four samples investigated are AlGaN/GaN heterostructure without a GaN cap layer (reference sample) and three other samples with GaN/AlGaN/GaN heterostructures in which the different thickness of GaN cap layer (2.7 nm, 7.5 nm, and 12.4 nm) has been considered. The sheet carrier density (n<SUB>s</SUB>) of a two-dimensional electron gas has decreased significantly from 4.66x10<SUP>12</SUP> cm<SUP>-2</SUP> to 2.15x10<SUP>12</SUP> cm<SUP>-2</SUP> upon deposition of a GaN capping layer (12.4 nm) over the reference structure. Through the analysis of internal fields in each GaN capping and AlGaN barrier layers, it has been concluded that the undiminished surface donor states (n<SUB>s</SUB>) of a reference structure and the reduced n<SUB>s</SUB> caused by the Au gate metal are approximately 5.66x10<SUP>12</SUP> cm<SUP>-2</SUP> and 1.08x10<SUP>12</SUP> cm<SUP>-2</SUP>, respectively.

Effect of electron-beam irradiation on leakage current of AlGaN/GaN HEMTs on sapphire

Oh, Seung Kyu,Song, Chi Gyun,Jang, Taehoon,Kwak, Joon Seop The Institute of Electronics and Information Engin 2013 Journal of semiconductor technology and science Vol.13 No.6

This study examined the effect of electron-beam (E-beam) irradiation on the electrical properties of n-GaN, AlGaN and AlGN/GaN structures on sapphire substrates. E-beam irradiation resulted in a significant decrease in the gate leakage current of the n-GaN, AlGaN and HEMT structure from $4.0{\times}10^{-4}A$, $6.5{\times}10^{-5}A$, $2.7{\times}10^{-8}A$ to $7.7{\times}10^{-5}A$, $7.7{\times}10^{-6}A$, $4.7{\times}10^{-9}A$, respectively, at a drain voltage of -10V. Furthermore, we also investigated the effect of E-beam irradiation on the AlGaN surface in AlGaN/GaN heterostructure high electron mobility transistors(HEMTs). The results showed that the maximum drain current density of the AlGaN/GaN HEMTs with E-beam irradiation was greatly improved, when compared to that of the AlGaN/GaN HEMTs without E-beam irradiation. These results strongly suggest that E-beam irradiation is a promising method to reduce leakage current of AlGaN/GaN HEMTs on sapphire through the neutralization the trap.

Effect of electron-beam irradiation on leakage current of AlGaN/GaN HEMTs on sapphire

오승규,송치균,장태훈,곽준섭 대한전자공학회 2013 Journal of semiconductor technology and science Vol.13 No.6

This study examined the effect of electron-beam (E-beam) irradiation on the electrical properties of n-GaN, AlGaN and AlGN/GaN structures on sapphire substrates. E-beam irradiation resulted in a significant decrease in the gate leakage current of the n-GaN, AlGaN and HEMT structure from 4.0×10-4 A, 6.5×10-5 A, 2.7×10-8 A to 7.7×10-5 A, 7.7×10-6 A, 4.7×10-9 A, respectively, at a drain voltage of -10V. Furthermore, we also investigated the effect of E-beam irradiation on the AlGaN surface in AlGaN/GaN heterostructure high electron mobility transistors(HEMTs). The results showed that the maximum drain current density of the AlGaN/GaN HEMTs with E-beam irradiation was greatly improved, when compared to that of the AlGaN/GaN HEMTs without E-beam irradiation. These results strongly suggest that E-beam irradiation is a promising method to reduce leakage current of AlGaN/GaN HEMTs on sapphire through the neutralization the trap.

사다리꼴 게이트 구조를 갖는 고내압 AlGaN/GaN HEMT

김재무(Jae-Moo Kim),김수진(Su-Jin Kim),김동호(Dong-Ho Kim),정강민(Kang-Min Jung),최홍구(Hong Goo Choi),한철구(Cheol-Koo Hahn),김태근(Tae-Geun Kim) 대한전자공학회 2009 電子工學會論文誌-SD (Semiconductor and devices) Vol.46 No.4

본 논문에서는 항복 전압 특성을 향상시키기 위한 사다리꼴 게이트 구조의 AlGaN/GaN HEMT구조를 제안하였으며 그 실현 가능성을 2차원 소자 시뮬레이터를 통해 조사하였다. 사다리꼴 게이트 구조의 사용으로 드레인 방향의 게이트 모서리 부근에서 나타나는 전계의 집중을 효과적으로 분산되는 것이 시뮬레이션 결과에서 확인 되었다. 제안된 사다리꼴 게이트 AlGaN/GaN HEMT 소자 구조에서 2DEG 채널을 따라 형성되는 전계의 피크값은 4.8 MV/㎝ 에서 3.5 MV/㎝ 로 기존 구조의 AlGaN/GaN HEMT에 비해 30 % 가량 감소하였으며, 그 결과로 인해 항복 전압은 49 V 에서 69 V 로 40 % 가량 증가하였다. We propose a trapezoidal gate AlGaN/GaN high electron mobility transistor (HEMT) to improve the breakdown voltage characteristics and its feasibility is investigated by two-dimensional device simulations. The use of a trapezoidal gate structure appears to be quite effective in dispersing the electric fields concentrated near the gate edge on the drain side from the simulation result. We find that a peak value of the electric field along the 2-DEG channel is reduced by 30 %, from 4.8 to 3.5 MV/㎝, and thereby, the breakdown voltage (Vbr) of the proposed AlGaN/GaN HEMT is increased by about 40 %, from 49 to 69 V, compared to those of the standard AlGaN/GaN HEMT.

Al0.3Ga0.7N/GaN 및 Al0.3Ga0.7N/GaN/Al0.15Ga0.85N/GaN 이종접합 구조에서 운반자 구속 효과와 이차원 전자가스의 광학적 특성

곽호상,이규석,조현익,이정희,조용훈 한국진공학회 2008 Applied Science and Convergence Technology Vol.17 No.4

금속 유기화학 증착기 (metal-organic chemical vapor deposition)를 이용하여 사파이어 기판 위에 Al0.3Ga0.7N/GaN 및 Al0.3Ga0.7N/GaN/Al0.15Ga0.85N/GaN 이종접합 구조들을 성장하고, 이들 시료의 전자와 정공들 간의 구속 효과를 조사하기 위하여 광학적, 구조적 특성을 비교하였다. 저온 (10 K) photoluminescence 실험으로부터 Al0.3Ga0.7N/GaN 단일 이종접합 구조의 경우 3.445 eV에서 단일의 이차원 전자가스 (two-dimensional electron gas; 2DEG) 관련된 발광을 관찰한 반면, Al0.3Ga0.7N/GaN/Al0.15Ga0.85N/GaN 다중 이종접합 구조의 경우 3.445 eV에서 뿐만 아니라, 3.42 eV에서 추가적인 2DEG 관련된 발광을 관찰 할 수 있었다. 이 두 개의 2DEG 관련 신호들의 근원을 조사하기 위하여 Al0.3Ga0.7N/GaN/Al0.15Ga0.85N/GaN 다중 이종접합구조에서의 에너지 밴드 구조를 이론적으로 계산하여 실험과 비교한 결과, 하나의 2DEG에 의한 서로 다른 버금띠로 부터가 아닌 다중 구조에 형성된 두 개의 2DEG로부터의 신호로 해석되었다. We have investigated optical and structural properties of Al0.3Ga0.7N/GaN and Al0.3Ga0.7N/GaN/Al0.15Ga0.85N/GaN heterostructures (HSs) grown by metal-organic chemical vapor deposition, by means of Hall measurement, high-resolution X-ray diffraction, and temperature- and excitation power-dependent photoluminescence (PL) spectroscopy. A strong GaN band edge emission and its longitudinal optical phonon replicas were observed for all the samples. At 10 K, a 2DEG-related PL peak located at ~ 3.445 eV was observed for Al0.3Ga0.7N/GaN HS, while two 2DEG peaks at ~ 3.42 and ~ 3.445 eV were observed for Al0.3Ga0.7N/GaN/Al0.15Ga0.85N/GaN HS due to the additional Al0.15Ga0.85N layers. Moreover, the emission intensity of the 2DEG peak was higher in Al0.3Ga0.7N/GaN/Al0.15Ga0.85N/GaN HS than in Al0.3Ga0.7N/GaN HS probably due to an effective confinement of the photo-excited holes by the additional Al0.15Ga0.85N layers. The 2DEG-related emission intensity decreased with increasing temperature and disappeared at temperatures above 150 K. To investigate the origin of the new 2DEG peaks, the energy-band structure for multiple AlGaN/GaN HSs were simulated and compared with the experimental data. As a result, the observed high- and low-energy peaks of 2DEG can be attributed to the spatially-separated 2DEG emissions formed at different AlGaN/GaN heterointerfaces.

압전 및 자발 분극을 고려한 단채널 AlGaN/GaN HEMT의 전류-전압 특성에 관한 해석적 모델

오영해,지순구,서정하,Oh Young-Hae,Ji Soon-Koo,Suh Chung-Ha 대한전자공학회 2005 電子工學會論文誌-SD (Semiconductor and devices) Vol.42 No.12

In this paper, in order to derive the current-voltage characteristics of n-AlGaN/GaN HEMTs with the piezoelectric and spontaneous polarizations, we suggested analytical solutions for the two-dimensional Poisson equation in the AlGaN and GaN regions by taking into account the longitudinal field variation, field-dependent mobility, and the continuity condition of the channel current flowing in the quantum well. Obtained expressions for long and short channel devices would be applicable to the entire operating regions in a unified manner. Simulation results show that the drain saturation current increases and the cutoff voltage decreases as drain voltage increases. Compared with the conventional models, the present model seems to provide more reasonable explanation for the drain-induced threshold voltage roll-off and the channel length modulation effect. 본 논문에서는 압전 및 자발 분극 효과를 내포한 단채널 n-AlGaN/GaN HEMT의 전류-전압 특성을 도출하고자 AlGaN 및 GaN층 내에서 분극을 고려한 2차원 Poisson 방정식의 해법을 제안하였다. AlGaN 및 GaN층에서의 2차원적 전위 변화를 채널전류의 연속조건과 컨시스턴트하게 도출하기 위해서 GaN영역에 형성된 양자 우물을 통해 흐르는 전자에 대한 전계-의존 이동도를 고려하였다. 도출된 표현식은 동작 전압 전 영역과 장/단채널 소자에 대하여 일괄적으로 적용될 수 있을 것으로 보이며, 계산 결과로부터 2차원 전위 분포 변화 효과를 고려하기 위한 파라미터 ${\alpha}$의 도입이 타당함을 보이고 있다. 이로써, 본 모델은 기존의 모델에 비해 드레인 전압의 증가에 따른 드레인 포화전류의 증가 및 문턱 전압의 감소 현상 등을 보다 적절히 설명할 수 있음을 보이고 있다.