A Band-Gap Energy Model of the Quaternary Alloy In_(x)Ga_(y)Al_(1−x−y)N using Modified Simplified Coherent Potential Approximation

Based on modification of the simplified coherent potential approximation,a model for the band-gap energy of In_(x)Ga_(y)Al_(1−x−y)N is developed.The parameters of the model are obtained by fitting the experimental band-gap energy of their ternary alloys.It is found that the results agree with the experimental values better than those reported by others,and that the band-gap reduction of In_(x)Ga_(y)Al_(1−x−y)N with increasing In or Ga content is mainly due to enhanced intraband coupling within the conduction band,and separately within the valence band.

High-Efficiency InGaN/GaN Nanorod Arrays by Temperature Dependent Photoluminescence

We report on the photoluminescent characteristics of InGaN/GaN multiple quantum well(MQW)nanorod arrays with high internal quantum efficiency.The InGaN/GaN MQWs are grown by metalorganic chemical vapor deposition on c-plane sapphire substrates,and then the MQW nanorod arrays are fabricated by using inductively coupled plasma etching with self-assembled Ni nanoparticle mask with low-damage etching technique.The typical diameter of the nanorods is from 200 nm to 300 nm and the length is around 800 nm,which almost is dislocation free.At room temperature,an enhancement of 3.1 times in total integrated photoluminescence intensity is achieved from the MQW nanorod arrays,in comparison to that of the as-grown MQW structure.Based on the temperature-dependent photoluminescence measurements,the internal quantum efficiency of the nanorod structure is 59.2%,i.e.,1.75 times of as-grown MQW structure(33.8%).Therefore,the nanorod structure with a significant reduction of defects can be a very promising candidate for highly efficient light emitting devices.

The Formation and Characterization of GaN Hexagonal Pyramids

GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method.Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviolet illumination,producing submicron-sized pyramids.Hexagonal pyramids on the etched GaN with well-defined{1011}facets and very sharp tips are formed.High-resolution x-ray diffraction shows that etched GaN with pyramids has a higher crystal quality,and micro-Raman spectra reveal a tensile stress relaxation in GaN with pyramids compared with normal GaN.The cathodoluminescence intensity of GaN after etching is significantly increased by three times,which is attributed to the reduction in the internal reflection,high-quality GaN with pyramids and the Bragg effect.

Influence of Dry Etching Damage on the Internal Quantum Efficiency of Nanorod InGaN/GaN Multiple Quantum Wells

The influence of dry etching damage on the internal quantum efficiency of InGaN/GaN nanorod multiple quantum wells (MQWs) is studied.The samples were etched by inductively coupled plasma (ICP) etching via a selfassembled nickel nanomask,and examined by room-temperature photoluminescence measurement.The key parameters in the etching process are rf power and ICP power.The internal quantum efficiency of nanorod MQWs shows a 5.6 times decrease substantially with the rf power increasing from 3W to 100W.However,it is slightly influenced by the ICP power,which shows 30% variation over a wide ICP power range between 30W and 600W.Under the optimized etching condition,the internal quantum efficiency of nanorod MQWs can be 40% that of the as-grown MQW sample,and the external quantum efficiency of nanorod MQWs can be about 4 times that of the as-grown one.

Enhanced Light Output of InGaN-Based Light Emitting Diodes with Roughed p-Type GaN Surface by Using Ni Nanoporous Template

Roughened surfaces of light-emitting diodes(LEDs)provide substantial improvement in light extraction efficiency.By preparing the self-assemble nanoporous Ni template through rapid annealing of a thin Ni film,followed by a low damage dry etching process,a p-side-up LED with a roughened surface has been fabricated.Compared to a conventional LED with plane surface,the light output of LEDs with nanoporous p-GaN surface increases up to 71%and 36%at applied currents of 1 mA and 20 mA,respectively.Meanwhile,the electrical characteristics are not degraded obviously after surface roughening.

Growth and Properties of Blue and Amber Complex Light Emitting InGaN/GaN Multi-Quantum Wells

Blue-red complex light emitting InGaN/GaN multi-quantum well(MQW)structures are fabricated by metal organic chemical vapor deposition(MOCVD).The structures are grown on a 2-inch diameter(0001)oriented(c−face)sapphire substrate,which consists of an approximately 2-µm−thick GaN template and a five-period layer consisting of a 4.9-nm-thick In0.18Ga0.82N well layer and a GaN barrier layer.The surface morphology of the MQW structures is observed by an atomic force microscope(AFM),which indicates the presence of islands of several tens of nanometers in height on the surface.The high resolution x−ray diffraction(XRD)θ/2θscan is carried out on the symmetric(0002)of the InGaN/GaN MQW structures.At least four order satellite peaks presented in the XRD spectrum indicate that the thickness and alloy compositions of the individual quantum wells are repeatable throughout the active region.Besides the 364 nm GaN band edge emission,two main emissions of blue and amber light from these MQWs are found,which possibly originate from the carrier recombinations in the InGaN/GaN QWs and InGaN quasi-quantum dots embedded in the QWs.