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With the emergence of a multichip Light-emitting diodes (LEDs) device based on different chip arrays, a new modeling for a multichip LED device with different array becomes urgent. This paper presents a compact thermal model (CTM) for the multichip LED device with different chip array for nonuniform thermal properties. Based on a general 3-D CTM, LED chips can be arranged in various array forms according to the multichip LED construction design. By linking the thermal matrix to junction temperature prediction, the proposed CTM provides accurate predictions of temperature distribution of the multichip LED device, compared to the practical physical model and infrared radiation measurement. The modeling technique has been successfully demonstrated and verified. Based on the proposed method, this paper presents the multichip LED device with a staggered array to optimize the LED positions so that heat concentration of the LED array can be reduced.

InGaN-based multiple quantum wells (MQWs) yellow light-emitting diodes (LEDs) were grown on Si substrate by metal organic vapor deposition. Blue MQWs were introduced as strain modulation layers for yellow MQWs. The LED chips emitted 72-mW yellow light with 566-nm dominant wavelength and 9.4 % external quantum efficiency (EQE) at 350 mA under room temperature, and it reached a peak EQE of 22.2 % at 0.7 mA. A comparison sample without strain modulation layers exhibited much weaker performance. The results reveal that long-wavelength emission of InGaN system is reliable if the strain of MQWs has been properly modulated.

Ni thin layer was deposited to assist to activate p-GaN and then was removed. The process was named Ni-assisted annealing (NA). We investigate the surface morphology and p-type contact behaviors of InGaN LED films grown on Si (1 1 1) substrates. Compared with conventional thermal annealing (TA), NA can improve the p-type contact characteristic at lower anneal temperature and a smaller specific contact resistivity ( ρ c = 6.1 × 10 −5 Ω cm 2 ) employing nonalloy Pt electrode was obtained. A wet etching method using acid–hydrogen peroxide was adopted to boil films surface after activation. We found that some nano-pits appeared on surfaces while original surface step structure was still clearly visible, which shows a defect-selective etching characteristic. Otherwise, we demonstrated that the surface morphology could be affected by NA while independent to TA. Some mechanisms for experimental phenomena were also discussed in the letter.

We report on the crystallographic tilting of AlN/GaN layers grown on Si (111) substrates with different miscut angles toward [110] direction. The inclination angle of the Si (111), AlN (002) and GaN (002) planes to the sample surface was measured by high resolution X-ray diffraction. We found that the tilt angles of the AlN and GaN layers with respect to the Si (111) plane are significantly larger than that predicted by the classical Nagai model. We proposed that in-plane mismatch played an important role in the tilt epitaxy of AlN/GaN layers on miscut Si (111) substrate.

High-quality ZnO films were grown on Si(1 1 1) substrate by MOCVD using a thin AlN buffer layer. A low-temperature ZnO buffer layer was further introduced to accommodate the lattice mismatch and thermal expansion coefficient mismatch between the ZnO epitaxial layer and the AlN buffer layer. In situ laser reflectance measurements show that two-dimensional growth has been obtained, and a smooth surface morphology is demonstrated by atomic force microscopy (AFM) measurements. X-ray diffraction (XRD) results show that the ZnO film is a single crystal. The FWHMs of (0 0 2) and (1 0 2) ω -scans for the 2.1 μm thick layer are 410 and 1321 arcsec, respectively. Free excitonic emission can be observed at low temperature and becomes dominant in the photoluminescence spectra above 120 K.

Properties of some GaN layers with different blue luminescence relative intensity were investigated by photoluminescence, Rutherford backscattering/channeling and double crystal X-ray diffraction, respectively. The surface minimum yields χ min of Rutherford backscattering/channeling and the FWHM of double crystal X-ray diffraction obviously increase with the increase of the intensity ratio of the blue luminescence to the band-edge emission. The blue luminescence is due to some intrinsic defects that can largely deteriorate the crystalline quality of GaN films. The luminescence mechanism of the blue luminescence in unintentional doped GaN films is different from that of the blue luminescence about 2.9 eV in GaN:Mg films.

The growth of Si-doped GaN films was performed by MOCVD using a homemade reactor operating at atmospheric pressure on (0 0 0 1) oriented sapphire. A study of the effect of Si-doping indicated that the intensity of yellow band emission in GaN : Si films decreased with the increasing of SiH4/TMGa ratio, and it was largely influenced by the parasitic reactions in the gas phase. The yellow band intensity was depressed when the parasitic reactions were reduced. We also observed that the growth rate of GaN : Si films was influenced by the Si doping and the parasitic reactions. The growth rate decreased with the increase of SiH4/TMGa ratio and was larger in larger parasitic reactions reactor. Sidoped GaN films with carrier concentration of 2 10 19 cm @3 , electron mobility of 120 cm 2 /V s, FWHM of the bandedge emission of only 60 meV at room temperature, and no yellow emission were obtained. r 2001 Elsevier Science

InGaN multiple quantum well (MQW) light-emitting diodes (LEDs), grown by metalorganic chemical vapor deposition (MOCVD) on Si (1 1 1) substrates, were successfully bonded and transferred onto new Si substrate. After chemical etching Si substrate and inductively coupled plasma (ICP) etching buffer layer, vertical structure GaN blue LEDs were fabricated. The characteristics of the lateral structure LEDs (grown on Si substrate) and the vertical structure LEDs (bonded on new Si substrate) have been investigated, and the performance of the vertical structure LEDs have obviously been improved compared to the lateral structure LEDs. The improved performance is due to the smaller tensile stress and series resistance in the vertical LEDs than that in lateral LEDs. The electroluminescence difference between vertical LEDs chips and the vertical LEDs lamps can be explained by the difference in heat dissipation.

MgSe thin films have been grown by metal-organic chemical vapor deposition on GaAs substrates. Our experimental results show that the crystal structure of MgSe depends strongly on both the growth temperature and the substrate orientation. Using the X-ray diffraction technique, we observed the three phases of MgSe; the rock salt, wurtzite and zincblende structures. The lattice constant of zincblende MgSe was determined to be 5.96 A.

The unintentional carbon doping concentration of GaN films grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) depends strongly on the growth rate. The concentration of carbon is varied from 2.9 × 10 17 to 5.7 × 10 18 cm -3 when the growth rate increases from 2.0 to 7.2 μ m/h, as detected by secondary ion mass spectroscopy. It is shown that the presence of N vacancies give rises to high carbon concentration. We show that a reduction of the carbon concentration by one order of magnitude compared to the regular sample with nearly same growth rate can be achieved by operating at an extremely high NH 3 partial pressure during growth. The intensity ratios of yellow and blue luminescence to band edge luminescence in the samples are found to depend significantly on carbon concentration. The present results demonstrate direct and quantitative evidence that the carbon related defects are the origin of yellow and blue luminescence.

After nearly ten years of exploration, our team firstly had a breakthrough in the technologies of materials growth and thin film chip manufacturing for high efficiency GaN based blue LED on silicon substrate in the world. The internal quantum efficiency and extraction efficiency of the vertical structure blue LED chips reached 80%. These LED chips have been realized mass production, and been successfully used in street lamps, miners lamp, down light, bulb light, flashlight and display imaging etc. In this paper, the related key technologies are comprehensive and systematically introduced. Selective-Area-Growth and Maskless-Micro-Epitaxial-Lateral-Overgrowth technologies were invented, by which a high crystalline quality GaN film was achieved with an only 100 nm AlN buffer layer. A set of systemic technologies were invented for manufacturing vertical thin film structure LED on silicon substrate, included high reflectance low resistance P type ohmic contact electrode, high stability low resistance N type electrode ohmic contact, surface roughening, complementary electrode, releasing residual tensile stress of GaN film technologies etc. At 350 mA (35 A/cm2), the light output power of blue LED (450 nm) on silicon is 657 mW, and external quantum efficiency of it is 68.1%.

InGaN/GaN multi-quantum well (MQW) light emitting diodes with heavily Mg doped and unintentionally doped (UID) low-temperature Al0.2Ga0.8N electron blocking layer (EBL) were investigated. Broad short-wavelength electroluminescence peak, which has strong relative intensity to the main emission, was found in the UID-EBL sample at cryogenic temperatures. Study suggests that the broad peak is emitted by the sidewall MQWs. This result indicates that the electroluminescence of sidewall MQWs, in which the carrier density is high enough, can be detected at cryogenic temperatures. The lineshape variation with current density reveals detailed information on the process of carrier injection into the sidewall MQWs.

InGaN/GaN multiple quantum well (MQW) light emitting diodes were grown on silicon substrate by metal organic chemical vapor deposition. A different barrier was heavily doped with silicon based on the same structure. Temperature dependent electroluminescence was performed on the devices. The results reveal that heavily doping the barrier distant from the n-type layer with silicon causes two emission peaks. As the doped barrier gets closer to n-type layer, the energy gap between the two peaks becomes narrower. Silicon doped in the barrier is believed to generate p-n junction built-in field from the doped barrier towards p-type layer. This field compensates the piezoelectric field in the well(s) between the doped barrier and p-type layer. It results in higher emission energy of this (these) well(s). When the doped barrier gets closer to the n-type layer, the compensation is less significant.

Crack free GaN films were grown on 1200×1200μm2 patterned Si (111) substrates and 36 light emitting diodes (LEDs) were fabricated in each pattern unit. Spatial distribution of the tensile stress in the pattern units and its influence on the LED performance are studied by micro-Raman and electroluminescence (EL). The Raman shift of the GaN E2 mode shows that the tensile stress is the maximum at the center, partially relaxed at the edge, and further relaxed at the corner. With the stress relaxation, the EL wavelength has a significant blue shift and the luminous intensity shows a great enhancement.