等离子体表面处理对硅衬底GaN基蓝光发光二极管内置n型欧姆接触的影响

硅衬底GaN基发光二极管(LED)的内置n型欧姆接触在晶圆键合时的高温过程中常常退化,严重影响LED的工作电压等器件性能.本文深入研究了内置n电极蒸镀前对n-GaN表面的等离子体处理工艺对硅衬底GaN基发光二极管n型欧姆接触特性的影响.实验结果表明,1.1 mm×1.1 mm的LED芯片在350 m A电流下,n-GaN表面未做等离子体处理时,n电极为高反射率Cr/Al的芯片正向电压为3.43 V,比n电极为Cr的芯片正向电压高0.28 V.n-GaN表面经O2等离子体表面处理后,Cr/Al和Cr电极芯片的正向电压均有所降低,但Cr/Al电极芯片的正向电压仍比Cr电极芯片高0.14 V.n-GaN表面经Ar等离子体处理后,Cr/Al电极芯片正向电压降至Cr电极芯片的正向电压,均为2.92 V.利用X射线光电子能谱对Ar等离子体处理前后的n-GaN表面进行分析发现,Ar等离子体处理增加了n-GaN表面的N空位(施主)浓度,更多的N空位可以提高n型欧姆接触的热稳定性,缓解晶圆键合的高温过程对n型欧姆接触特性的破坏.同时还发现,经过Ar等离子体处理并用HCl清洗后,n-GaN表面的O原子含量略有增加,但其存在形式由以介电材料GaO_x为主转变为导电材料GaO_xN_(1-x)和介电材料GaO_x含量相当的状态,这会使得接触电阻进一步降低.上述两方面的变化均有利于降低LED芯片的正向电压.

Thermal analysis of GaN laser diodes in a package structure

Using the finite-element method, the thermal resistances of GaN laser diode devices in a TO 56 package for both epi-up configuration and epi-down configuration are calculated. The effects of various parameters on the thermal characteristics are analysed, and the thicknesses of the AlN submount for both epi-up configuration and epi-down configuration are optimized. The obtained result provides a reference for the parameter selection of the package materials.

Thermal analysis of GaN-based laser diode mini-array

Thermal characteristics of multiple laser stripes integrated into one chip is investigated theoretically in this paper. The temperature pattern of the laser diode mini-array packaged in a TO-can is analyzed and optimized to achieve a uniform temperature distribution among the laser stripes and along the cavity direction. The temperature among the laser stripes varies by more than 5 K if the stripes are equally arranged, and can be reduced to less than 0.4 K if proper arrangement is designed. For conventional submount structure, the temperature variation along the cavity direction is as high as 7 K, while for an optimized trapezoid submount structure, the temperature varies only within 0.5 K.

A High Power InGaN-Based Blue-Violet Laser Diode Array with a Broad-Area Stripe

An array of high power InGaN/GaN multi-quantum-well laser diodes with a broad waveguide is fabricated.The laser diode structure is grown on a GaN substrate by metal-organic chemical vapor deposition.The laser diode array consists of five emitter stripes which share common electrodes on one laser chip.The electrical and optical characteristics of the laser diode array are investigated under the pulse current injection with 10 kHz frequency and 100 ns pulse width.The laser diode array emits at the wavelength of 409 nm,which is located in the blue-violet region,and the threshold current is 2.9 A.The maximum output light peak power is measured to be 7.5 W at the wavelength of 411.8 nm under the current of 25 A.

Formation of Low-Resistant and Thermally Stable Nonalloyed Ohmic Contact to N-Face n-GaN

We report on the formation of Ohmic contacts with low resistance and high thermal stability to N-face n-GaN for vertical structure light emitters using a Ti(50nm)/Pt(50nm)/Au(50nm)metal scheme,where the Pt layer is introduced as a blocking layer to suppress the diffusion of Au onto the N-face n-GaN surface.It is shown that unlike the conventional Ti/A1/Ti/Au contacts,the Ti/Pt/Au contacts exhibit an Ohmic behavior with a relatively low specific contact resistivity of 1.1×10^(-4)Ω.cm^(2) even after annealing at 350℃.X-ray diffraction(XRD)measurements by synchrotron radiation and Auger electron spectroscopy(AES)examination are performed to understand the effects of heat treatment.

GaN grown on nano-patterned sapphire substrates

High-quality gallium nitride （GaN） film was grown on nano-pattemed sapphire substrates （NPSS） and investigated using XRD and SEM. It was found that the optimum thickness of the GaN bulter layer on the NPSS is 15 nm, which is thinner than that on micro-patterned sapphire substrates （MPSS）. An interesting phenomenon was observed for GaN film grown on NPSS：GaN mainly grows on the trench regions and little grows on the sidewalls of the patterns at the initial growth stage, which is dramatically different from GaN grown on MPSS. In addition. the electrical and optical properties of LEDs grown on NPSS were characterized.

GaN-on-Si blue/white LEDs:epitaxy,chip,and package

The dream of epitaxially integrating III-nitride semiconductors on large diameter silicon is being fulfilled through the joint R＆D efforts of academia and industry, which is driven by the great potential of Ga N-onsilicon technology in improving the efficiency yet at a much reduced manufacturing cost for solid state lighting and power electronics. It is very challenging to grow high quality Ga N on Si substrates because of the huge mismatch in the coefficient of thermal expansion（CTE） and the large mismatch in lattice constant between Ga N and silicon, often causing a micro-crack network and a high density of threading dislocations（TDs） in the Ga N film.Al-composition graded Al Ga N/Al N buffer layers have been utilized to not only build up a compressive strain during the high temperature growth for compensating the tensile stress generated during the cool down, but also filter out the TDs to achieve crack-free high-quality n-Ga N film on Si substrates, with an X-ray rocking curve linewidth below 300 arcsec for both（0002） and（10N12） diffractions. Upon the Ga N-on-Si templates, prior to the deposition of p-Al Ga N and p-Ga N layers, high quality In Ga N/Ga N multiple quantum wells（MQWs） are overgrown with well-engineered V-defects intentionally incorporated to shield the TDs as non-radiative recombination centers and to enhance the hole injection into the MQWs through the via-like structures. The as-grown Ga N-on-Si LED wafers are processed into vertical structure thin film LED chips with a reflective p-electrode and the N-face surface roughened after the removal of the epitaxial Si（111） substrates, to enhance the light extraction efficiency. We have commercialized Ga N-on-Si LEDs with an average efficacy of 150–160 lm/W for 1mm^2 LED chips at an injection current of 350 m A, which have passed the 10000-h LM80 reliability test. The as-produced Ga N-on-Si LEDs featured with a single-side uniform emission and a nearly Lambertian distribution can adopt the wafer-level phosphor coating procedure, and are suitable for directional lighting, camera flash, streetlighting, automotive headlamps, and otherlighting applications.