GaN基LED光电器件的磊层研究与设计

介绍了一种缓解GaN基LED效率下降的器件设计方法,重点研究了采用新方法光电器件中载流子的分布。根据与传统GaN器件的对比,可以发现LED效率提高的原因是空穴的浓度分布的更加均匀。     

Investigation of radiative tunneling in GaN/InGaN single quantum well light-emitting diodes

The mechanisms of carrier injection and recombination in a GaN/InGaN single quantum well light-emitting diodes have been studied. Strong defect-assisted tunneling behavior has been observed in both forward and reverse current–voltage characteristics. In addition to band-edge emission at 400 nm, the electroluminescence has also been attributed to radiative tunneling from band-to-deep level states and band-to-band tail states. The approximately current-squared dependence of light intensity at 400 nm even at high currents indicates dominant nonradiative recombination through deep-lying states within the space-charge region. Inhomogeneous avalanche breakdown luminescence, which is primarily caused by deep-level recombination, suggests a nonuniform spatial distribution of reverse leakage in these diodes.     

生长压力对GaN材料光学与电学性能的影响

研究了采用MOCVD技术分别在100与500Torr反应室压力下生长的非故意掺杂GaN薄膜的光学与电学性能。研究表明,低压100Torr外延生长条件可以有效地降低Ga与NH3气相反应造成GaN薄膜的碳杂质沾污,从而抑制造成光致发光中黄光峰与蓝光峰的深受主的形成,所制备的材料表现出较好的光学性能。同时,不同生长压力下的GaN薄膜表现出相异的电学性能,即在500Torr下生长的样品通常表现出更高的载流子浓度（（4.6-6.4）×1016 cm-3）与更高的迁移率（446-561cm2/（V.s））,而100Torr下生长的样品通常表现为更低的载流子浓度（1.56-3.99）×1016 cm-3与更低迁移率（22.9-202cm2/（V.s））。     

GaN HFET沟道热电子隧穿电流崩塌模型

研究了GaN HFET中沟道热电子隧穿到表面态及表面态电子跃迁到表面导带两种跃迁过程及其激活能.从沟道热电子隧穿过程出发,提出了新的电流崩塌微观模型.用该微观模型解释了光离化谱、DLTS、瞬态电流及电流崩塌等各类实验现象.研究了各种异质结构的不同电流崩塌特性,在此基础上讨论了无电流崩塌器件的优化设计.     

AlGaN/GaN HFET中的陷阱位置和激活能

自洽求解薛定谔方程和泊松方程求出了异质结能带和沟道阱基态、激发态及二维表面态的波函数.研究了 表面陷阱位置及其激活能.发现表面高密度缺陷减薄了势垒层,显著增强了热电子隧穿过程.从缺陷态发射电子和 热电子隧穿构成的新陷阱模型出发,解释了HFET的瞬态电流和产生.复合噪声.最后讨论了改进材料生长和器件 工艺来抑制陷阱效应,改善器件性能的途径.     

p型InGaN/GaN超晶格N面GaN基LED的光电特性

随着氮(N)面GaN材料生长技术的发展,基于N面GaN衬底的高亮度发光二极管(LED)的研究具有重要的科学意义.研究了具有高发光功率的N面GaN基蓝光LED的新型结构设计,通过在N面LED的电子阻挡层和多量子阱有源层之间插入p型InGaN/GaN超晶格来提高有源层中的载流子注入效率.为了对比N面GaN基LED优异的器件性能,同时设计了具有相同结构的Ga面LED.通过对两种LED结构的电致发光特性、有源层中能带图、电场和载流子浓度分布进行比较可以发现,N面LED在输出功率和载流子注入效率上比Ga面LED有明显的提升,从而表明N面GaN基LED具有潜在的应用前景.     

Properties of GaN epitaxial layers grown on 6H-SiC(0001) by plasma-assisted molecular beam epitaxy

The structural, electrical, and optical properties of GaN grown on 6H-SiC(0001) substrates by molecular beam epitaxy are studied. Suitable substrate preparation and growth conditions are found to greatly improve the structural quality of the films. Threading dislocation densities of about 3×10⁹ cm⁻² for edge dislocations and <1×10⁶ cm⁻² for screw dislocations are achieved in GaN films of 0.8 μm thickness. Mechanisms of dislocation generation and annihilation are discussed. Increasing the Ga to N flux ratio used during growth is found to improve the surface morphology. An unintentional electron concentration in the films of about 5×10¹⁷ cm⁻³ is observed, and is attributed to excess Si in the films due to a Si-cleaning step used in the substrate preparation. Results from optical characterization are correlated with the structural and electronic studies.     

Si和Si-Ge结中不同带带隧穿模型的对比研究

We compared several different band-to-band tunneling(BTBT) models with both Sentaurus and the two-dimensional full-band Monte Carlo simulator in Si homo-junctions and Si-Ge hetero-junctions. It was shown that in Si homo-junctions, different models could achieve similar results. However, in the Si-Ge hetero-junctions, there were significant differences among these models at high reverse biases(over 2 V). Compared to the nonlocal model, the local models in Sentaurus underrated the BTBT rate distinctly, and the Monte Carlo method was shown to give a better approximation. Additionally, it was found that in the Si region near the interface of the Si-Ge hetero-junctions, the direct tunneling rates increased largely due to the interaction of the band structures of Si and Ge.     

击穿电压提高的AlGaN/GaN/AlGaN双异质结特性

本文论述了AlGaN/GaN双异质结高电子迁移率晶体管的特性,该结构使用Al组分为7%的AlGaN来代替传统的GaN作为缓冲层。Al0.07Ga0.93N缓冲层增加了二维电子气沟道下方的背势垒高度,有效提高了载流子限阈性,从而造成缓冲层漏电的显著减小以及击穿电压的明显提高。对于栅尺寸为0.5100μm,栅漏间距为1μm的器件,AlGaN/GaN 双异质结器件的击穿电压（~100V）是常规单异质结器件的两倍（~50V）。本文中的双异质结器件在漏压为35V、频率为4GHz下,最大输出功率为7.78W/mm,最大功率附加效率为62.3%,线性增益为23dB。     

Study of electrically active defects in n-GaN layer

Deep level defects in both p⁺/n junctions and n-type Schottky GaN diodes are studied using the Fourier transform deep level transient spectroscopy. An electron trap level was detected in the range of energies at E_c−E_t=0.23–0.27 eV with a capture cross-section of the order of 10⁻¹⁹–10⁻¹⁶ cm² for both the p⁺/n and n-type Schottky GaN diodes. For one set of p⁺/n diodes with a structure of Au/Pt/p⁺–GaN/n–GaN/n⁺–GaN/Ti/Al/Pd/Au and the n-type Schottky diodes, two other common electron traps are found at energy positions, E_c−E_t=0.53–0.56 eV and 0.79–0.82 eV. In addition, an electron trap level with energy position at E_c−E_t=1.07 eV and a capture cross-section of σ_n=1.6×10⁻¹³ cm² are detected for the n-type Schottky diodes. This trap level has not been previously reported in the literature. For the other set of p⁺/n diodes with a structure of Au/Ni/p⁺–GaN/n–GaN/n⁺–GaN/Ti/Al/Pd/Au, a prominent minority carrier (hole) trap level was also identified with an energy position at E_t−E_v=0.85 eV and a capture cross-section of σ_n=8.1×10⁻¹⁴ cm². The 0.56 eV electron trap level observed in n-type Schottky diode and the 0.23 eV electron trap level detected in the p⁺/n diode with Ni/Au contact are attributed to the extended defects based on the observation of logarithmic capture kinetics.     

量子点发光器件的制备与仿真分析

为研究量子点发光器件结构与性能的关系,制备了以CdSe/ZnS量子点作为发光层、poly-TPD作为空穴传输层,Alq3作为电子传输层的量子点发光二极管,对器件结构及性能参数进行了表征,结果显示器件具有开启电压低、色纯度高等特点.结合测试数据,对量子点发光二极管进行了器件结构建模,利用隧穿模型及空间电荷限制电流模型对实验结果进行了分析,研究了器件中载流子的注入与传输机理.器件测试与仿真结果表明:各功能层厚度会影响载流子在量子点层的注入平衡,同时器件中载流子的注入与传输存在一转变电压,当外加电压低于转变电压时,器件中载流子的注入主要符合隧穿模型;当外加电压高于转变电压时,器件中载流子的注入主要符合空间电荷限制电流模型.研究结果验证了器件结构建模的合理性,可以利用仿真的方法进行器件结构优化并确定相关参数,这对器件性能的提高具有指导意义.     

微型化太赫兹集成器件的前沿技术进展

针对国际上太赫兹器件技术进展予以概括和分析,提炼出共振隧穿二极管、单向载流子传输光电二极管2种可行的小型化器件方案。在材料生长和器件结构方面分析了太赫兹波的产生原理和难点,在系统应用方面解释了短距离高速通信的实用案例。目前,采用共振隧穿二极管已实现2.5 Gbps速率的300 GHz无线通信演示实验,采用单向载流子传输光电二极管在该频点下实现了12.5 Gbps的无线通信实验。