Growth of InGaN and double heterojunction structure with InGaN back barrier

We study the growth of an InGaN and AIGaN/GaN/InGaN/GaN double heterojunction structure by metalorganic chemical vapor deposition (MOCVD).It is found that the crystal quality of the InGaN back barrier layer significantly affects the electronic property of the AIGaN/GaN/InGaN/GaN double heterojunction.A high crystal quality InGaN layer is obtained by optimizing the growth pressure and temperature.Due to the InGaN layer polarization field opposite to that in the AIGaN layer,an additional potential barrier is formed between the GaN and the InGaN layer,which enhances carrier confinement of the 2DEG and reduces the buffer leakage current of devices.The double heterojunction high-electron-mobility transistors with an InGaN back barrier yield a drain induced barrier lowering of 1.5 mⅤ/Ⅴ and the off-sate source-drain leakage current is as low as 2.6μA/mm at VDs = 10 Ⅴ.     

预应变InGaN/GaN多量子阱发光特性调控研究

为了减弱InGaN/GaN量子阱内的压电极化场,在蓝紫光InGaN/GaN多量子阱激光器结构中采用了预应变InGaN插入层,通过变温电致发光和高分辨X射线衍射测量研究了预应变插入层对量子阱晶体质量和发光特性的影响。实验结果显示,常温下有预应变层的量子阱电致发光谱积分强度显著提高。模拟计算进一步表明,预应变层对量子阱内压电极化场有调制效果,有利于量子阱中的应力弛豫,可以有效减弱量子限制斯塔克效应,有助于提高量子阱的发光效率。     

InGaN/GaN和InGaN/AlGaN多量子阱中应变对光致发光特性的影响

对蓝宝石衬底上的InGaN/GaN和InGaN/AlGaN多量子阱结构和经激光剥离去除衬底的InGaN/GaN和InGaN/AlGaN多量子阱结构薄膜样品,进行了光致发光谱、高分辨XRD和喇曼光谱测量.PL测量结果表明,相对于带有蓝宝石衬底的样品,InGaN/GaN多量子阱薄膜样品的PL谱峰值波长发生较小的蓝移,而InGaN/AlGaN多量子阱薄膜样品的PL谱峰值波长发生明显的红移;喇曼光谱的结果表明,激光剥离前后E2模的峰值从569.1减少到567.5cm-1.这说明激光剥离去除衬底使得外延层整体的压应力得到部分释放,但InGaN/GaN与InGaN/AlGaN多量子阱结构中阱层InGaN的应力发生了不同的变化.XRD的结果证实了这一结论.     

MOCVD生长的全组分InGaN材料

利用金属有机物化学气相淀积(MOCVD)方法在C面蓝宝石衬底上制备了全组分InGaN薄膜,通过改变生长温度和In/Ga比例成功调控了InGaN合金组分和带隙宽度。利用不同的物理表征手段系统研究了InGaN薄膜的晶体结构和光电学性质,XRD和Hall等测试结果表明:富Ga的InGaN薄膜具有较好的晶体质量,背景电子浓度基本均比富In的InGaN低一个数量级。同时,结合光致发光谱和光学透射谱研究了InGaN合金带隙随In组分的变化关系。     

Al在生长InGaN材料中的表面活化效应

为了解决材料的界面平整度,改善材料的晶体质量,在Ⅲ-Ⅴ族氮化物(InGaN)材料的生长过程中,加入了Al掺杂剂.实验发现,InGaN材料的双晶衍射半宽从533arcsec(非掺Al)下降到399 arcsec(轻掺Al),PL光谱半宽变窄,从21.4 nm(非掺Al)降为20.9 nm(轻掺Al).研究结果表明,Al作为活性剂明显提高了InGaN材料质量,这将对改善LED和LD多量子阱材料和器件质量带来积极影响,目前还没有相关的文献报道.     

高质量立方相InGaN的生长

利用 LP- MOCVD技术在 Ga As( 0 0 1 )衬底上生长了高质量的立方相 In Ga N外延层 .研究了生长速率对 In Ga N质量的影响 ,提出一个简单模型解释了在改变 TEGa流量条件下出现的In组分的变化规律 ,实验结果与模型的一次项拟合结果较为吻合 ,由此推断 ,在现在的生长条件下 ,表面单个 Ga原子作为临界晶核吸附 Ga或 In原子实现生长的模型与实际情况较为接近 .对于晶体质量的变化也给予了说明 .得到的高质量立方相 In Ga N室温下有很强的发光峰 ,光致发光峰半高宽为 1 2 8me V左右 .     

InGaN/GaN heterostructures grown by submonolayer deposition

InGaN/(Al,Ga)N heterostructures containing ultrathin InGaN layers, grown by submonolayer deposition are studied. It is shown that significant phase separation with the formation of local In-enriched regions ??3?C4 nm in height and ??5?C8 nm in lateral size is observed in InGaN layers in the case of InGaN and GaN growth by cyclic deposition to effective thicknesses of less than one monolayer. The effect of growth interruption in a hydrogen-containing atmosphere during submonolayer growth on the structural and optical properties of InGaN/(Al,Ga)N heterostructures is studied. It is shown that these interruptions stimulate phase separation. It is also shown that the formation of In-enriched regions can be controlled by varying the effective InGaN and GaN thicknesses in the submonolayer deposition cycles.     

Wide-gap semiconductor InGaN and InGaAln grown by MOVPE

We have achieved InGaN growth on sapphire substrates at temperatures substantially higher than conventional growth temperatures for InGaN. When the growth temperature was changed from 500 (conventional) to 800° C (this work) in InGaN, the x-ray diffraction line width (full width at half maximum) decreased from 100 to 30 min. At 77 K, edge emission was observed in PL. In order to further improve crystalline quality, we have investigated ZnO as a lattice-matching substrate. First, the surface treatment and the resistance to the reducing atmosphere at high temperatures was briefly investigated. We report the first successful lattice-matched growth of InGaN. The x-ray diffraction line width of InGaN grown on ZnO was about 20% smaller than that of films grown on sapphire substrates, thus using lattice-matched substrates was shown to have an effect on improving the crystalline quality of InGaN. Single crystal InGaAlN has been also realized on sapphire substrates. The indium, gallium and aluminum contents were 2.2, 22.5 and 74.3%, respectively. The optical transmission characteristic of this InGaAlN was measured.     

超高亮度InGaN单量子阱结构绿色LED

发光强度为１２ｃｄ的超高亮度绿色ＩｎＧａＮ单量子阱（ＳＱＷ）结构发光二极管已研制成功。该器件的输出功率、外量子效率、峰值波长和光谱半宽在正向电流２０ｍＡ下分别为３ｍＷ、６．３％、５２０ｎｍ和３０ｎｍ。这种绿色ＩｎＧａＮ单量子阱发光二极管的Ｐ－Ａｌ－ＧａＮ／ＩｎＧａＮ／ｎ－ＧａＮ是用ＭＯＣＶＤ方法生长在蓝宝石衬底上。     

Visible InGaN/GaN Quantum-Dot Materials and Devices

General properties of III-V nitride-based quantum dots (QDs) are presented, with a special emphasis on InGaN/GaN QDs for visible optoelectronic devices. Stranski-Krastanov GaN/AlN dots are first discussed as a prototypical system. It is shown that the optical transition energies are governed by a giant quantum-confined Stark effect, which is the consequence of the presence of a large built-in internal electric field of several MV/cm. Then we move to InGaN/GaN QDs, reviewing the different fabrication approaches and their main optical properties. In particular, we focus on InGaN dots that are formed spontaneously by In composition fluctuations in InGaN quantum wells. Finally, some advantages and limitations of nitride laser diodes with active regions based on InGaN QDs are discussed, pointing out the requirements on dot uniformity and density in order to be able to exploit the expected quantum confinement effects in future devices.     

Self-pulsation in an InGaN laser-theory and experiment

Room-temperature operation of self-pulsating InGaN lasers was obtained at a wavelength of 395 nm. The laser structure consists of a multiquantum-well InGaN active layer and a p-type InGaN single-quantum-well saturable absorber. The frequency range of the self-pulsation was from 1.6 to 2.9 GHz. The experimental results were well explained with our theoretical analysis. We found that features of the saturable absorber strongly affect the self-pulsation. Influence of device and material parameters on the laser dynamics was also investigated.     

MOCVD生长的InGaN薄膜中的相分离

利用X射线衍射(XRD)测量用MOCVD生长的In Ga N样品,观察到In N相.通过X射线衍射理论,计算得到In N相在In Ga N中的含量.通过退火和变化生长条件发现In N相在In Ga N薄膜中的含量与生长时N2 载气流量、反应室压力和薄膜中存在的应力有关.进一步的分析表明In Ga N合金中出现In N相的主要原因是相分离.     

Spontaneous Emission and Characteristics of Staggered InGaN Quantum-Well Light-Emitting Diodes

A novel gain media based on staggered InGaN quantum wells (QWs) grown by metal-organic chemical vapor deposition was demonstrated as improved active region for visible light emitters. Fermi's golden rule indicates that InGaN QW with step-function like In content in the well leads to significantly improved radiative recombination rate and optical gain due to increased electron-hole wavefunction overlap, in comparison to that of conventional InGaN QW. Spontaneous emission spectra of both conventional and staggered InGaN QW were calculated based on energy dispersion and transition matrix element obtained by 6-band k middotp formalism for wurtzite semiconductor, taking into account valence-band-states mixing, strain effects, and polarization-induced electric fields. The calculated spectra for the staggered InGaN QW showed enhancement of radiative recombination rate, which is in good agreement with photoluminescence and cathodoluminescence measurements at emission wavelength regime of 425 and 500 nm. Experimental results of light-emitting diode (LED) structures utilizing staggered InGaN QW also show significant improvement in output power. Staggered InGaN QW allows polarization engineering leading to improved luminescence intensity and LED output power as a result of enhanced radiative recombination rate.     

Numerical simulation of InGaN Schottky solar cell

The Indium Gallium Nitride (InGaN) III-Nitride ternary alloy has the potentiality to allow achieving high efficiency solar cells through the tuning of its band gap by changing the Indium composition. It also counts among its advantages a relatively low effective mass, high carriers' mobility, a high absorption coefficient along with good radiation tolerance. However, the main drawback of InGaN is linked to its p-type doping, which is difficult to grow in good quality and on which ohmic contacts are difficult to realize. The Schottky solar cell is a good alternative to avoid the p-type doping of InGaN. In this report, a comprehensive numerical simulation, using mathematically rigorous optimization approach based on state-of-the-art optimization algorithms, is used to find the optimum geometrical and physical parameters that yield the best efficiency of a Schottky solar cell within the achievable device fabrication range. A 18.2% efficiency is predicted for this new InGaN solar cell design.     

Phase separation in Zn-doped InGaN grown by metalorganic chemical vapor deposition

Zn-doped InGaN thin films were deposited on GaN/sapphire by metalorganic chemical vapor deposition, and studied by a combination of high-resolution X-ray diffraction (HR-XRD), micro-photoluminescence (PL) and secondary ion mass spectrometry (SIMS). Indium phase separation is studied comparatively. HR-XRD exhibits a GaN band and a single band from InGaN for samples without phase separation, but two InGaN bands corresponding to different x(In) for samples with phase separation. PL excitation power dependence measurements reveal 2 sets of InGaN PL emissions for samples with phase separation, but only 1 set for samples without phase separation. SIMS data showed that phase separated InGaN:Zn films possess a high Zn concentration near the InGaN–GaN interface and non-uniform distributions of In and Zn contents, which are in contrast with data from InGaN:Zn films with no In-phase separation.     

LP－MOCVD生长InGaN单晶薄膜

报道了以Ａｌ２Ｏ３为衬底在ＧａＮ薄膜上ＬＰ－ＭＯＣＶＤ外延生长ＩｎＧａＮ单晶薄膜，并研究了ＩｎＧａＮ的生长特性。实验给出了ＩｎｘＧ１－ｘＮ合金的固相组分与汽相组分和生长温度的变化关系，并应用Ｘ射线衍射（ＸＲＤ）、Ｘ射线回摆曲线（ＸＲＣ）和室温光致荧光（ＰＬ）谱等技术对外延层的晶体质量、完整性和发光特性进行了分析。发现ＩｎＧａＮ／ＧａＮ系统中保持适当的压应力有助于提高外延层的晶体完整性，减少非故意掺杂杂质的引入，能改善外延层的发光特性。     

InGaN LEDs still headlining

Just a few years ago blue-green LEDs were an expensive curiosity with little practical application owing to their inferior price/performance. While the opto industry was making millions of low-cost longer wavelength LEDs, the blue emitters were lagging far behind. However, all that has changed and recently we were treated to an intriguing ironic twist: two of the world's opto leaders were almost coincidentally making announcements that overlapped each other's areas of interest. While Nichia was demonstrating InGaN amber LEDs, HP was gearing up for InGaN blue-green LEDs.     

Growth of InGaN HBTs by MOCVD

The design and growth of GaN/InGaN heterojunction bipolar transistors (HBTs) by metalorganic chemical vapor deposition (MOCVD) are studied. Atomic-force microscopy (AFM) images of p⁺InGaN base layers (∼100 nm) deposited under various growth conditions indicate that the optimal growth temperature is limited to the range between 810 and 830°C due to a trade-off between surface roughness and indium incorporation. At these temperatures, the growth pressure must be kept above 300 Torr in order to keep surface pit density under control. An InGaN graded-composition emitter is adopted in order to reduce the number of V-shaped defects, which appear at the interface between GaN emitter and InGaN base and render an abrupt emitter-base heterojunction nearly impossible. However, the device performance is severely limited by the high p-type base contact resistance due to surface etching damage, which resulted from the emitter mesa etch.     

InGaN光致发光性质与温度的关系

分析了用金属有机物气相外延方法(MOVPE)在蓝宝石衬底上生长的铟镓氮(InGaN)的光致发光(PL)性质.发现在4.7K至300K范围内,随着温度升高,InGaN带边辐射向低能方向移动,峰值变化基本符合Varshni经验公式;同时InGaN发光强度虽有所衰减,但比GaN衰减程度小,分析了导致GaN和InGaN光致发光减弱的可能因素.     

Optical Properties of Silicon—doped InGaN and GaN Layers

The optical properties of Silicon—doped InGaN and GaN grown on sapphire by MOCVD have been investigated by photoluminescence (PL) method. At room temperature, the band—gap peak of InGaN is 437.0 nm and its full width of half—maximum (FWHM) is about 14.3 nm. The band—gap peak and FWHM for GaN are 364.4 nm and 9.5 nm, respectively. By changing the temperature from 20 K to 293 K, it is found that the PL intensity of samples decreases but the FWHM broadens with the increasing of the temperature.GaN sample shows red—shift, InGaN sample shows red—blue—red—shift. The temperature dependence of peak energy shift is studied and explained.