Indium-Induced Effect on Polarized Electroluminescence from InGaN/GaN MQWs Light Emitting Diodes

Polarization-resolved edge-emitting electroluminescence （EL） studies of In GaN/GaN MQWs of wavelengths from near-UV （390nm） to blue （468nm） light-emitting diodes （LEDs） are performed. Although the TE mode is dominant in all the samples of InGaN/GaN MQW LEDs, an obvious difference of light polarization properties is found in the InGaN/GaN MQW LEDs with different wavelengths. The polarization degree decreases from 52.4% to 26.9% when light wavelength increases. Analyses of band structures of InGaN/GaN quantum wells and luminescence properties of quantum dots imply that quantum-dot-like behavior is the dominant reason for the low luminescence polarization degree of blue LEDs, and the high luminescence polarization degree of UV LEDs mainly comes from QW confinement and the strain effect. Therefore, indium induced carrier confinement （quantum-dot-like behavior） might play a major role in the polarization degree change of InGaN/GaN MQW LEDs from near violet to blue.     

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     

Mosaic Structure Evolution in GaN Films with Annealing Time Grown by Metalorganic Chemical Vapour Deposition

We investigate mosaic structure evolution of GaN films annealed for a long time at 800℃ grown on sapphire substrates by metalorganic chemical vapour deposition by high-resolution x-ray diffraction. The result show that residual stress in GaN films is relaxed by generating edge-type threading dislocations （TDs） instead of screw-type TDs. Compared to as-grown GaN films, the annealed ones have larger mean twist angles corresponding to higher density of edge-type TDs but smaller mean tilt angles corresponding to lower density of screw-type TDs films. Due to the increased edge-type TD density, the lateral coherence lengths of the annealed GaN films also decrease. The results obtained from chemical etching experiment and grazing-incidence x-ray diffraction （GIXRD） also support the proposed structure evolution.     

Effect of annealing on photoluminescence and microstructures of InGaN／GaN multi-quantum well with Mg-doped p-type GaN

InGaN/GaN multi-quantum well structure with Mg-doped p-type GaN was grown by low-pressure metalorganic vapour phase epitaxy. After rapid-thermal-annealing at 700 and 900${^\circ}$C, both the red-shift and the blue-shift of the photoluminescence (PL) peak, the decreased and the enhancement of the PL intensity were observed. The transmission electron microscopic images showed that InGaN multi-quantum-dots-like (MQD-like) structures with dimensions less than 5$\tm$10nm were formed in InGaN wells. The changes of PL spectra could be tentatively attributed to the competition between the red-shift mechanism of the quantum-confined Stark effect and the blue-shift mechanism of the quantum size effect due to MQD-like structures.     

MOCVD生长InGaN/GaN MQW紫光LED

利用LP－MOCVD系统生长了InGaN/GaN MQW紫光LED外延片，双晶X射线衍射测试获得了2级卫星峰，室温光致发光谱的峰值波长为399.5nm，FWHM为15.5nm，波长均匀性良好。制成的LED管芯，正向电流20mA时，工作电压在4V以下。     

Influence of patterned TiO2/SiO2 dielectric multilayers for back and front mirror facetson GaN-based laser diodes

Ridge InGaN multi-quantum-well-structure （MQW） edge-emitting laser diodes （LDs） were grown on （0001） sapphire substrates by low-pressure metal-organic chemical vapour deposition （MOCVD）. The dielectric TiO2/SiO2 front and back facet coatings as cavity mirror facets of the LDs have been deposited with electron-beam evaporation method. The reflectivity of the designed front coating is about 50% and that of the back high reflective coating is as high as 99.9%. Under pulsed current injection at room temperature, the influences of the dielectric facets were discussed. The threshold current of the ridge GaN-based LDs was decreased after the deposition of the back high reflective dielectric mirrors and decreased again after the front facets were deposited. Above the threshold, the slope efficiency of the LDs with both reflective facets was larger than those with only back facets and without any reflective facets. It is important to design the reflectivity of the front facets for improving the performance of GaN-based LDs.     

用卢瑟福背散射/沟道技术及高分辨X射线衍射技术分析不同Al和In含量的AlInGaN薄膜的应变

利用卢瑟福背散射/沟道技术对在蓝宝石衬底上用金属有机化学气相沉积方法生长的有GaN缓冲层(>2μm)的一系列不同Al和In含量的AlInGaN薄膜进行组分及结晶品质的测量；并结合高分辨X射线衍射技术，通过对AlInGaN的对称(0002)面，及非对称(1015)面的θ—2θ扫描及倒空间扫描，可以精确测定AlInGaN外延层的晶格常数及水平和垂直方向的应变.实验结果表明AlInGaN 薄膜中不同含量Al和In对其应变有较大的影响，结合Vegard定理，对这一现象给出了理论的解释. 关键词： AlInGaN 高分辨X射线衍射 卢瑟福背散射/沟道 弹性应变     

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.     

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。     

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.