空气和氧气气氛下p-GaN/Ni/Au合金性质

研究了p-CaN上的Au／Ni双金属层在空气气氛和氧气气氛下合金对其欧姆接触性质的影响。使用同步辐射高强度X射线衍射观察到明显的NiO衍射峰。随着合金时间的增加,NiO和Au的结晶性均明显变好,NiO的衍射峰强度随合金时间的增加而增强,同时发现Au(111)沿CaN的(0001)面择优形成单晶。测得Ni／Au-p-CaN-Ni／Au串联电阻在合金后明显降低,表明接触性质改善与结晶性的提高有关。同时发现氧气下合金比空气下合金形成NiO更快,相应的串联电阻也更快地下降。     

Barrier Enhancement Effect of Postannealing in Oxygen Ambient on Ni/AIGaN Schottky Contacts

Al0.2 Ga0.8N/GaN samples are grown by metalorganic chemical vapour deposition （MOCVD） method on （0001） sapphire substrates. A 10nm-thick Ni layer is deposited on AlGaN as the transparent Schottky contact. The effect of postannealing in oxygen ambient on the electrical properties of Ni/AlGaN is studied by current-voltage- temperature （I-V-T） measurement. The annealing at a relatively low temperature of 300℃ for 90 s results in a decrease of the ideality factor from 2.03 to 1.30 and an increase of the Schottky barrier height from 0.77eV to 0.954 e V. The I-V-T analysis confirms the improvement originated from the formation of NiO, a layer with higher resistance, which could passivate the surface states of AlGaN and suppress the tunnelling current. Furthermore, the annealing also leads to an increase of the transmittance of the contacts from 57.5% to 78.2%, which would be favourable for A1GaN-based photodetectors.     

Electrical Characteristics of InGaN/AlGaN and InGaN/GaN MQW Near UV-LEDs

Electrical characteristics of In0.05 Ga0.95N/Al0.07Ga0.9aN and In0.05 Ga0.95N/GaN multiple quantum well （MQW） ultraviolet light-emltting diodes （UV-LEDs） at 400hm wavelength are measured. It is found that for InGaN/AlGaN MQW LEDs, both ideality factor and parallel resistance are similar to those of InGaN/GaN MQW LEDs, while series resistance is two times larger. It is suggested that the Al0.07Ga0.93N barrier layer did not change crystal quality and electrical characteristic of p-n junction either, but brought larger series resistance. As a result, InGaN/AlGaN MQW LEDs suffer more serious thermal dissipation problem although they show higher light output efficiency.     

Effect of Indium Ambient on Electrical Properties of Mg-Foped AlxGa1-xN

Mg-doped AlxGa1-xN epilayers were grown on AlN/sapphire templates by metal organic chemical vapor depo- sition （MOCVD） using an indium-assisted growth method. At room temperature, the resistivity of Mg-doped Alo.43Gao.57N epilayer grown under indium （In） ambient is of the order of 10^4Ω.cm, while the resistivity of Mg-doped Al0.43Ga0.57N grown without In assistance is of the order of 10^6Ω.cm. The ultraviolet light-emitting diodes （UV-LEDs） using the In-assisted Mg-doped Al0.43Ga0.57N as the p-type layers were fabricated to verify the function of indium ambient. It is found that there are a lower turn-on voltage and a lower diode series resistance in the UV-LEDs fabricated with p-type Al0.43Ga0.57 N layers grown under In-ambient.     

Effects of fluorine-based plasma treatment and thermal annealing on high-Al content AlGaN Schottky contact

Fluorine plasma treatment was used prior to the Schottky metal deposition on the undoped Al_(0.45)Ga_(0.55)N,which aimed at the solar-blind wavelength.After fluorine plasma treatment and before depositing the Ni/Au Schottky,the samples were thermal annealed in the N_2 gas at 400 ℃.The reverse leakage current density of Al_(0.45)Ga_(0.55)N Schottky diode was reduced by 2 orders of magnitude at-10 V.The reverse leakage current density was reduced by 3 orders of magnitude after thermal annealing.Further capacitance-frequency analysis revealed that the fluorine-based plasma treatment reduces the surface states of AlGaN by one order of magnitude at different surface state energies.The capacitance-frequency analysis also proved that the concentration of carriers in AlGaN top is reduced through fluorine plasma treatment.     

Influence of applied electric field on the absorption coefficient and subband distances in asymmetrical AlN/GaN coupled double quantum wells

The influence of applied electric fields on the absorption coefficient and subband distances in asymmetrical AlN/GaN coupled double quantum wells (CDQWs) has been investigated by solving Schr?dinger and Poisson equations self-consistently. It is found that the absorption coefficient of the intersubband transition (ISBT) between the ground state and the third excited state (1_odd-2_even) can be equal to zero when the electric fields are applied in asymmetrical AlN/GaN CDQWs, which is related to applied electric fields induced symmetry recovery of these states. Meanwhile, the energy distances between 1_odd-2_even and 1_even-2_even subbands have different relationships from each other with the increase of applied electric fields due to the different polarization-induced potential drops between the left and the right wells. The results indicate that an electrical-optical modulator operated within the opto-communication wavelength range can be realized in spite of the strong polarization-induced electric fields in asymmetrical AlN/GaN CDQWs.     

Structural characterization of V/Al/V/Au Ohmic contacts to n-type Al0.4Ga0.6N

This paper investigates the temperature dependence of the specific resistance in annealed V/Al/V/Au (15 nm/85 nm/20 nm/95 nm) contacts on n-Al0.4Ga0.6 N. Contacts annealed at 700C and higher temperatures show Ohmic behaviour. Annealing at 800 C produces the lowest contact resistance. Samples annealed at 800C have been analysed by using cross-sectional transmission electron microscopy and an energy dispersive x-ray spectrum. Limited reaction depths are observed between V-based contacts and n-AlGaN. The VN grains are found to form in the contact layer of the annealed samples,which can be considered as the key to the successful formation of Ohmic contact. The contact layer adjacent to AlGaN material consists of V-Al-Au-N,AlN and AlAu alloys.     

高N2气流下在GaAs(001)上用MBE法生长InN

在N2 气压为 2 6 7× 10 -2 Pa ,5 0 0℃的条件下 ,用MBE方法在GaAs(0 0 1)衬底上生长了InN的外延层。生长期间 ,In流量以 3× 10 14 到 2 4× 10 14 atoms/cm2 ·s范围内变化。用X 射线衍射 (XRD)和反射高能电子衍射 (RHEED)法对InN膜进行了表征。发现在生长的初始阶段 ,所生长的InN属立方相 ,但随着外延层厚度的增加出现了InN层由立方相向六角相的相变。X 射线倒易空间图形测量表明的在GaAs(0 0 1)衬底上生长的六角相InN其c 轴主要沿GaAs的〈111〉B方向取向     

侧向外延法生长的高质量GaN及其外延缺陷的观察

在有条状SiO2图形的GaN“模板”上,侧向外延方法生长了高质量的GaN。荧光显微镜的结果表明在SiO2掩膜区有成核过程发生。原因可能是SiO2的质量不高,为GaN的生长提供了一些成核中心。在GaN层的厚度达到4．5μm后,侧向的融合开始发生。侧向生长的速度与垂直生长速度几乎相同。在所有的SiO：掩膜上方都形成了空洞。样品在240℃熔融的KOH中腐蚀13min。在SiO2掩膜区生长的GaN,其腐蚀坑密度(相当于穿透位错密度)减少到几乎为零。而在窗口区生长的GaN,腐蚀坑密度仍然很高,达到10^8cm^-2量级。同时,我们发现具有不同窗口尺寸的样品在SiO2掩膜区上侧向生长的CaN的晶体质量基本相同,与窗口区的宽度几乎无关。室温光荧光结果表明侧向外延法生长的CaN中的晶格失配应力已被部分释放。     

纳米压印制备的光子晶体结构对AlGaN基材料深紫外出光效率的提高

通过利用阳极氧化铝的方法制备高度有序的光子晶体结构作为纳米压印模板,将大面积光子晶体图案转移到了样品表面,解决了国际上小尺寸光子晶体制备困难的问题。采用纳米压印的方法在AlGaN基样品表面上制备了290 nm的周期光子晶体结构,并将表面具有光子晶体结构的AlGaN基样品正面出光强度提高121%。偏振特性的实验结果表明六角排列的孔状光子晶体将原来朝向样品侧面传播的TE偏振光偏折转向正面,从而增加光抽取效率,改变出光偏振度。指出远场角分辨图案的变化归因于光子晶体对出光的衍射和Bragg散射效果。实验中采用的创新性工艺可以用来制备具有高出光效率的深紫外发光二极管。