Search

In this work the effect of Si doped InGaN/GaN heterostructure is systematically studied. The n-InGaN/GaN heterostructure are grown on c-plane sapphire substrate by horizontal flow Metal Organic Chemical Vapor Deposition (MOCVD). The heterostructure samples are investigated by structural, optical, morphological and electrical studies using High Resolution X-ray diffraction (HRXRD), room temperature Photoluminescence (PL), Atomic Force Microscopy (AFM) and Hall measurement respectively. The composition of indium in n-InGaN/GaN heterostructure was calculated as 15.9% using epitaxy smooth fit software. The energy band gap (Eg) of the InGaN epilayer has been calculated as 2.78 eV using vigard's law. PL emission obtained at 446 nm for n-InGaN epilayer. AFM results indicate that the Si doped InGaN/GaN heterostructure has the root mean square (rms) roughness of about 0.59 nm for a scan area of 5x5 µm² which has island like growth. Moreover, Hall measurements results shows that Si doped InGaN/GaN heterostructure possess carrier concentration of 4.2 x 1018cm-3 and mobility of 257 cm²/V s at room temperature. [ABSTRACT FROM AUTHOR]

EMCORE grown and tested four-junction terrestrial concentrator inverted metamorphic multijunction (CIMM) devices have been demonstrated with internally measured typical efficiencies of ~44% and peak efficiencies as high as ~47%, which are in the realm of world record performance. Improved internal testing as well as external validation by NREL are in progress. [ABSTRACT FROM AUTHOR]

Different multifunctional (PbTiO3, Sm0.6Nd0.4NiO3, NdMnO3) thin films were grown by metalorganic chemical vapor deposition (MOCVD) technique on SrTiO3 and LaAlO3 substrates. TEM and X-ray diffraction measurements reveal that almost single crystalline thin films can be epitaxially grown on the top of substrates. The relationship between the crystallographic orientation of the films and those of the substrates were determined by reciprocal space mapping and TEM analyses. PbTi03 thin films appear to be under tensile or compressive strain according to the different mismatch of their cell parameter with those of the substrate. Relaxation mechanism as a function of the film thickness arises from coexistence of different type of domains and size and strain effect are analyzed. SmNiO3 thin films present diffuse scattering strikes and are less well organized when compared to PbTi03 thin films. Different domains are observed as well as an additional parasitic phase close to NiO. Its regular distribution can be associated to reduced transport properties. Preliminary observations on NdMnO3 thin films show that an amorphous phase is obtained during MOCVD that can be transformed in a single crystalline film by annealing. The films are under tensile or compressive strain according to the different mismatch of their cell parameter with those of the substrate. Magnetic properties are investigated. [ABSTRACT FROM AUTHOR]

AlInP/GaInP distributed Bragg-reflector (DBRs) were prepared by MOCVD. Influences of the flow velocity and rate of mixed gas on homogeneity of epitaxial film were investigated systematically. Compared with the change of single group V source, the uniformity of AlInP/GaInP layers was significantly improved by changing simultaneously the distribution of upper and lower nozzle group in the fixed V/III ratio. [ABSTRACT FROM PUBLISHER]

The crystal quality and structural properties of GaSb thin films grown on a semi-insulator GaAs (001) substrate by metalorganic chemical vapor deposition (MOCVD) using triethylgallium and trimethylantimony were characterized by high-resolution X-ray diffraction and high-resolution transmission electron microscopy. The nucleation of the interfacial misfit dislocations (IMF) array in the GaSb/GaAs interface, which is dependent on the antimony ambience, was investigated by varying the V/III ratio. Our experiment results showed that the IMF array and threading dislocation density are modified in the GaSb epilayer with different antimony ambiences. The GaSb thin film grown by the IMF mode on GaAs was confirmed under our optimal growth condition, and the hole density and mobility of GaSb thin films were found to be 5.27 × 1016 cm−3 (1.20 × 1016) and 553 cm2/V-s (2340) at RT (77 K) from Hall measurements. We suggest that the IMF growth mode can also be applied to fabricate the GaSb film on GaAs by MOCVD for application in microelectronic devices. [ABSTRACT FROM PUBLISHER]

GaP epitaxial layer was prepared by planetary MOVCD on 2°GaAs substrate. Use the XRD (X-ray diffraction) to test the full width at half maximum (FWHM) of rocking-curve and use the high power microscope to watch the crystal surface quality. Summary the growth condition of high-quality GaP epitaxial layer. The results show that the surface quality depends on high growth temperature and slow growth velocity. Perfect surface was obtained when the thickness that grow GaP epitaxial layer in low temperature and slow velocity is 20nm. [ABSTRACT FROM PUBLISHER]

We have developed a novel MOCVD reactor, which is called buffered distributed spray (BDS) MOCVD reactor, for the multiple wafer growth of films of III–V materials. In the present study, a fundamental and multi-field model based on the computational fluid dynamic (CFD) simulation of coupled flow, heat and mass transfer is presented to describe the epitaxial growth of gallium nitride (GaN). It is investigated how reactor geometry affects flow field, temperature profile, and concentration distribution. For comparison, a horizontal reactor with the same geometry is also modeled. The modeling results show that the BDS MOCVD reactor performs well in GaN growth. [ABSTRACT FROM PUBLISHER]

High-performance InAlN/GaN heterostructure by metal-organic chemical vapor deposition and field effect transistor with a nominal gate length of 0.2 μm on sapphire substrate were obtained. Low defects density and a high electron mobility of 1930 cm2/V·s were obtained for the heterostructure. The fabricated device exhibited remarkable RF characteristics, i.e. a cutoff frequency of 69GHz with the gate length of 0.2μm, suggesting the extraordinary performances reachable by InAlN based technology. [ABSTRACT FROM PUBLISHER]

Triple junction solar cells (TJSC) are the main components of concentrator photovoltaic (CPV) systems. Metalorganic chemical vapor deposition (MOCVD) is the manufacturing process of choice used to produce state of the art solar cells. An improvement in cell efficiency through improvement in cell design lowers the overall cost of solar electricity and stimulates widespread adoption of solar systems. Recently, the introduction of multiquantum well (MQW) structures into TJSC devices has been shown to improve short circuit currents and improve cell efficiency. [ABSTRACT FROM PUBLISHER]

The effect of growth temperature on InAs QDs grown by metal-organic chemical vapor deposition (MOCVD) was investigated in detail. Growth temperature affects InAs QDs in three ways, including the reconstruction mode of new InAs crystal faces, the migration length of adatoms, band gaps of InAs QDs, and the interaction among three aspects was studied. The variation of density, size and wavelength was experimentally demonstrated. The high density of 5.2×1010cm−2 was obtained. The room temperature wavelength of InAs/GaAs QDs using GaAs as capping layer reached 1240nm. [ABSTRACT FROM PUBLISHER]

Metal organic chemical vapor deposition (MOCVD) tools are integral to many technologies, including the growth of high-efficiency multijunction III-V solar cells. Veeco MOCVD has recently developed new tool designs that allow increased MOCVD growth rates that could drastically increase solar cell throughput and reduce manufacturing costs. It is important, however, to understand the trade-offs between increased throughput and decreased material quality and device performance. We fabricate multijunction III-V solar cells from materials grown by both standard and fast growth rate techniques. We analyze the open circuit voltage, short circuit current, fill factor, efficiency, and ideality factor of both types of devices. Comparison of these devices reveals that the existing fast growth protocols result in solar cells with similar performance to standard growth cells. The results suggest that increased growth rates can enable higher throughput fabrication of solar cells without significant performance sacrifices. [ABSTRACT FROM PUBLISHER]

The mechanism leading to RT ferromagnetism in Gd-doped GaN is not well understood. Oxygen impurities have been proposed as a possible contributor to ferromagnetic behavior in Ga1−xGdxN films but the physical mechanism is not clear. In this work, Ga1−xGdxN thin films were grown by MOCVD using two different metalorganic Gd precursors (TMHD)3Gd and Cp3Gd. Samples grown with (TMHD)3Gd, which contains oxygen, exhibited much higher magnetic moments. Co-doping of the Ga1−xGdxN films with Si produced conductive n-type material, while co-doping with Mg produced compensated p-type material. Si and Mg co-doped films exhibited room temperature ferromagnetism and this material was then incorporated into a room temperature spin-polarized LED. Electroluminescence from this device had a degree of polarization of 14.6% at 5000 Gauss and retained a degree of polarization of 9.3% after removal of the applied magnetic field. [ABSTRACT FROM PUBLISHER]

Germanium selenide (GexSe100-x with 0

Single layer of In0.5Ga0.5As quantum dots (QDs) was grown using self-assembled Stranski-Krastanow on a thin InxGa1-xAs underlying layer and on a reference GaAs wafer by metal-organic chemical vapour deposition (MOCVD). The effect of different indium composition in the underlying layer and the duration of arsine (AsH3) flow during cooling-down period of the growth process were investigated and characterized using atomic force microscopy (AFM). The growth of the thin underlying layer has significant influence on the formation of the QDs on the top surface. The dots density increases with increasing indium composition in the underlying layer. AsH3 flow during the period was found to influence the nucleation process of In0.5Ga0.5As QDs. A shorter period of AsH3 flow promotes smaller dots size and therefore increases the dots density. [ABSTRACT FROM AUTHOR]

In this work the effect of different concentration of Magnesium doped GaN (p-GaN) were systematically studied. The p-GaN epilayers were grown on c-plane sapphire substrate by horizontal flow Metal Organic Chemical Vapor Deposition (MOCVD) with various flow rates of 100 sccm to 300 sccm using bis-(cyclopentadienyl) - magnesium (Cp2Mg) precursor. The samples were subjected to structural, optical, morphological and electrical studies using High Resolution X-ray diffraction (HRXRD), room temperature photoluminescence (PL), Atomic Force Microscopy (AFM) and Hall measurement respectively. Results indicated that the Mg doped GaN of 200 sccm Cp2Mg has the root mean square (rms) roughness of about 0.3 nm for a scan area of 5x5 μm² which has good two dimensional growth. Moreover, Hall measurements results shows that (200 sccm Cp2Mg) Mg-doped GaN possess the highest hole concentration of 5.4x1017cm-3 and resistivity of 1.7 Ocm at room temperature. [ABSTRACT FROM AUTHOR]

Stacked InxGa1-xAs quantum dots (QDs) were grown by metal-organic chemical vapor deposition (MOCVD) via Stranski -Krastanov growth mode. AFM images show that the QDs structures were formed and the stacked structure of InxGa1-xAs QDs were confirmed by the HR-XRD analysis. Composition of the dots on the top most layers was related to the number of stack layers. The observed PL peak position was blue-shifted due to different number of stacked QDs. The PL intensity also dramatically increase, which shows the possibility of the QDs application in optical devices at room temperature [ABSTRACT FROM AUTHOR]

Ti1-xCOxO2 thin films have been grown on n-type Si(100) substrates by metal organic vapor deposition (MOCVD) using titanium (IV) isopropoxide (TTIP) and tris (2,2,6,6-tetramethyl-3, 5-heptanedionato) cobalt (III) as metal organic precursors. The parameter deposition, such as: bubbler temperature of TTIP Tb(Ti) = 50 °C; substrate temperature Ts = 450 °C; bubbler pressure Pb(Ti) = 260 Torr; flow rate of Ar gas through TTIP precursor Ar(Ti) = 100 sccm (standard cubic centimeters per minute) and flow rate of oxygen gas O2 = 60 sccm were found as optimal deposition parameters. The thin films deposited were have rutile (002) crystal plane, whereas those deposited at other parameter were mixing of anatase and rutile phases. Co dopant with concentration of up to 5.77% was not changes the structure of TiO2. Increase of Co incorporated in thin films was decreasing of band-gap energy. [ABSTRACT FROM AUTHOR]

Microstructure and optical properties of AlxGa1-xN/GaN heterostructures thin films grown on Si(111) substrate by Plasma Assisted-Metalorganic Chemical Vapor Deposition (PA-MOCVD) were investigated. The surface morphology and crystal orientation of the films were determined by scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. The content of Al in AlxGa1-xN films (x) was determined by means of NIR-UV visible optical reflectance spectroscope. The surface morphology of films depends significantly on the content of Al. Films with higher value of x showed the smaller grain size and the smoother surface. Films with x = 0.29 and x = 0.36 showed crystal orientation of (101_0) plane, while films with x = 0.12 have two crystal orientation of (101_0) and (101_1) planes. The optical reflectance spectra showed that the ordered of oscillation depend on the smoothness of the film surface, while the number of oscillation related to the thickness of films. The calculated band gap was 3.34 eV for GaN and in the range of 3.34 to 6.20 eV for AlxGa1-xN depending on the x values. [ABSTRACT FROM AUTHOR]

We present the local structural properties of ZnO nanorods studied by using extended x-ray absorption fine structure (EXAFS). Vertically aligned ZnO nanorods were fabricated on Al2O3 substrates by a catalyst free metal organic chemical vapor deposition (MOCVD). The polarized EXAFS measurements on the ZnO nanorods were performed at Zn K-edge. The polarized EXAFS study revealed that the nanorods had a wurtzite structure, and that there were substantial amount of structural disorders in Zn-O pairs in the beginning of the nanorod growth. The EXAFS measurements revealed that the orientation-dependent disorders of the Zn-O pairs were directly related to the growth mechanism and crystal quality of the ZnO nanorods. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The InGaN/GaN SQW structures were grown on c-plane sapphire substrate using metal-organic chemical vapor deposition (MOCVD). The thickness and indium composition of the InGaN was determined by HRXRD. From simulation fit the composition of indium was found to be 10% and thickness was around 5nm and 10nm. The Photoluminescence emission was found to be shifited towards lower wavelength as 479nm, 440nm on increasing the thickness. The photoluminescence intensity was degrades with increases of InGaN thickness. Atomic force microscopy studies were also carried out and the results are discussed in detail. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) nanowalls have been epitaxially grown on dislocation assisted GaN/Al2O3 template by metal organic chemical vapor deposition (MOCVD) without any help of metal catalysts. A large number of nanowalls with thicknesses of 1.5-2.0 μm and height 400 nm have been deposited. The AlN nanowalls were found to have a preferred c-axis oriented with a hexagonal crystal structure. The AlN nanowalls and GaN/Al2O3 template have been characterize at room temperature photoluminescence (PL) and high resolution X-ray diffraction (HRXRD). [ABSTRACT FROM AUTHOR]

AlGaN/AlN layers were grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. The AlxGa1-xN layer composition was varied from 15% to 25%. The crystalline quality, thickness and aluminum (Al) composition of AlGaN were determined using high resolution X-ray diffraction (HRXRD). The growth rate decreases on increasing Al composition. Reciprocal space mapping (RSM) was used to estimate the strain and relaxation between AlGaN and AlN. The optical properties of AlGaN layers were investigated by room temperature Photoluminescence (PL). The AlGaN peak shifts towards lower wavelength with Al composition. The surface morphology of AlGaN was studied by atomic force microscopy (AFM). Root mean square (RMS) roughness values were found to be increased in AlGaN layers with composition. [ABSTRACT FROM AUTHOR]

AlGaInP LEDs with Coupled distributed bragg reflectors were grown by Metal-organic Chemical Vapor Deposition (MOCVD). The results showed that the peak wavelength of this structure LED was 625nm, and normal luminous intensity was increased to 164mcd on injection current 20mA from the LED with coupled DBR structure. [ABSTRACT FROM PUBLISHER]

For observation of parasitic reaction effect during InAlN material growth by Matel-Organic Chemical Vapor Deposition (MOCVD), the growth parameters include temperature and pressure had been varied to investigate it. The pressure would be kept at 50torr, 100torr and 150torr and temperature was varied from 700 °C to 780 °C by 20 °C step in each growth pressure. The experimental results appeared that higher pressure gave rise to more serious parasitic reaction during material growth. It made the less Al atoms incorporate into the AllnN. In addition the 100-torr growth pressure shows the best efficiency of Al atom incorporation compare with other two growth pressures. By the AFM analysis, the morphology of Al0.82In0.18N grown with three different pressures was also examined. [ABSTRACT FROM PUBLISHER]

We demonstrate butt-coupled p-i-n InGaAs photodetectors epitaxially grown on silicon substrates by MOCVD. We measure a dark current of 8 nA upon −1V and open eye-diagrams at 15Gb/s upon −3V and at 20Gb/s upon −5V. [ABSTRACT FROM PUBLISHER]

In this work, we present nanostructured core-shell solar cells based on patterned GaAs nanopillars grown by MOCVD.[1] The patterns are photolithographically defined and center-to-center pitch, hole size and mask arrangement can be pre-determined at nanometric resolution. The inherently catalyst-free growth mode eliminates any metal (i.e. Au) diffusion into the nanopillars that could hinder the electron-hole pair extraction. The lattice-matched growth capability also avoids threading dislocations that normally act as recombination centers, worsening the leakage current in pn-junction based devices. [ABSTRACT FROM PUBLISHER]

The growth conditions of GaxIn1−xAsyP1−y lattice-matched to GaAs using MOCVD on (001) oriented substrates are analyzed. The epitaxial layer composition is varied from GaAs to lattice-matched Ga0.52In0.48P via quaternary grade. The layer quality is more sensitive to experimental variables as the composition approaches the Ga0.52In0.48P side than when growing quaternaries. TEM images show promising results even though the top layer Ga0.52In0.48P needs to be further optimized. The fundamental objective of this work is to improve understanding over the growth of LMM alloys on GaAs with special emphasis on quaternary grades. We believe that incorporation of LMM quaternaries with ternaries in a single-junction device will provide flexibility in design which may ultimately lead to record PV conversion efficiencies. [ABSTRACT FROM PUBLISHER]

A study of leakage currents and X-ray photon counting using GaAs p-i-n diodes is presented. Different fabrication techniques have been investigated, namely He implantation, partial wet etching and full wet etching. It was found that the partially etched diodes showed well-defined spectral peaks when exposed to a 55Fe radioisotope source and uniformly low leakage currents ideal for X-ray detector arrays. [ABSTRACT FROM PUBLISHER]

We discuss compositional and structural transmission electron microscopy (TEM) characterization of lattice-mismatched (LMM) III-V epilayers grown on GaAs by metalorganic chemical vapor deposition (MOCVD), with possible applications in high-efficiency multijunction solar cells. In addition to the use of TEM imaging to survey layer thicknesses and defect morphology, our analysis emphasizes the particular methods of energy-dispersive X-ray spectrometry (EDX) and convergent-beam electron diffraction (CBED). Outlined here is a standards-based method for extracting compositions by EDX, which uses principal-component analysis (PCA) [1], combined with the zeta-factor approach of Watanabe and Williams [2]. A procedure is described that uses the coordinates of high-order Laue zone (HOLZ) lines, which are found in the bright-field disks of CBED patterns, to extract composition and strain parameters from embedded epilayers. The majority of the crystal growth for this work was performed at NREL, which has accommodated the development at SDSM&T of the characterization techniques described. However, epilayer deposition capability at SDSM&T has recently been achieved, using a home-built system, which is presently being used to examine new lattice-mismatched structures relevant to photovoltaic technology. [ABSTRACT FROM PUBLISHER]

As scientific technology makes progress, there are more and more applications of mixture gas in semiconductor, flat panel display, LED MOCVD and solar manufacturing process. The request of mixture gas criteria is more critical than before, especial on precise concentration control, impurity control and high volume gas supply under safe condition. In order to meet customer's request, Praxair (PX) has developed the novel method of filling mixture gas for TFT LCD and LED MOCVD doping process. It includes two kinds of filling method for different applications in TFTLCD and LED MOCVD doping process. For TFT LCD process, PX has developed on-site high volume blending system of 1% PH3/H2 mixture gas for TFT LCD n+ a-Si doping process & it has been qualified by Taiwan customer. The on-site blending system can provide high volume, more tighten concentration control, more reliable on gas supply, reduces gas cylinder change frequency and lowest cost of ownership. PX on-site blending system uses pure PH3 cylinder and H2 gas (customer supply) to form 1% PH3/H2 mixture by dynamic MFC control through in-situ concentration sensor feedback. The blending system has excellent performance of PH3 concentration control & has reached mean value 1.0002%, stdev 0.0128% performance by customer on-site demo. The performance is 6X better than customer target. The blending system has been proved and qualified by small, middle and large batches mass production and shows comparable result on process, device, yield, RA performance in comparison with current supplier (gas cylinder or toner package). The other method of filling SiH4 or Si2H6 mixture is for LED MOCVD nGaN doping process. PX has developed the concentration analysis system and it can analyze the concentration from two digital percentage levels until ppm level. In general, it uses traditional gravimetric method for filling SiH4 or SiH4 mixture and needs 4 ∼ 6 filling steps(depend on balance gas) to reach ppm level. Due to lots of filling steps, it causes propagation error in filling steps and can't control mixture gas concentration precisely. It also causes lots of cost and working labor on filling process. PX has developed the novel method for concentration analysis and reduces filling steps from 4∼6 steps to 2∼3 steps for ppm concentration level. Due to less filling steps, it reduces the propagation error and gets better concentration control products. For example, 200 ppm Si2H6/H2 mixture gas cylinder concentration spec. is +/− 10% by using traditional gravimetric method, PX can reach gas cylinder concentration spec. +/− 5% by using new method. The tighten concentration spec. cylinders can reduce or skip test-run time after cylinder change & provide more consistent concentration control within batch to batch cylinders. The new method is not only for SiH4 or Si2H6 mixture in LED MOCVD process & it can extend to others process gas like GeH4/H2 mixture in advance semiconductor EPI process or other applications. [ABSTRACT FROM PUBLISHER]

Diblock copolymer lithography followed by selective growth is used for the nanofabrication of InGaAs quantum dots (QDs) on InP substrate. Stronger photoluminescence intensity is observed when in-situ CBr4 etching is employed prior to QD growth. [ABSTRACT FROM PUBLISHER]

This work presents a pioneering study on the MOCVD droplet epitaxy of strain-free GaAs/Al0.3Ga0.7As quantum molecules. By choosing the appropriate growth conditions, GaAs quantum molecules can be obtained with controlled size and density. The formation of these molecules is mainly due to the anisotropic migration of Ga adatoms and the edge enhanced crystallization process. Furthermore, these molecules show excellent optical properties, suggesting their promising applications in devices such as infrared photodetectors and quantum information processing. [ABSTRACT FROM PUBLISHER]

We report on growth of GaAs nanowires on Si(111) substrates using Ga droplets by metal-organic chemical vapour deposition (MOCVD). Appropriate growth conditions to achieve stabilization of small Ga droplets as well as Ga-assisted VLS growth of GaAs nanowires were found. This work facilitates comparative studies of crystalline quality and nanowire surfaces as a function of the droplet (catalyst) material. [ABSTRACT FROM PUBLISHER]

InxGa1−xAs nanowires were grown using metal-organic chemical vapour deposition (MOCVD) with various growth temperatures and V/III ratios. The morphology of these nanowires and the composition distribution along the nanowire were studied as a function of these growth parameters. With higher growth temperature and lower V/III ratio, the tapering of the nanowires is reduced. However, the incorporation of Ga in the nanowires is also reduced with lower V/III ratio. The composition distribution along the nanowires is non-uniform with typically In-rich bases and Ga-rich tips. [ABSTRACT FROM PUBLISHER]

Quantum dot solar cells can potentially realize ultrahigh efficiencies in single p-n junction structures utilizing intermediate-level energy bands. However, so far most fabricated quantum dot solar cells have suffered from severe reduction of open-circuit voltage by incorporation of quantum dots resulting in significantly lower efficiencies than those without quantum dot. Here we fabricate a high-efficiency InAs/GaAs quantum dot solar cell. Our cell contains five layers of high-density (4 × 1010 cm−2 per layer) self-assembled InAs quantum dots grown by metalorganic chemical vapor deposition suppressing open-circuit-voltage degradation. We develop a dual-layer anti-reflection coating of optimum thicknesses. The resulting cell exhibits efficiencies of 18.7% under AM1.5G, 1 sun and 19.4% for 2 suns, the highest reported thus far, for any kind of quantum dot cell. Our high-efficiency demonstration in a cell grown by MOCVD is a strong encouragement towards the commercialization of quantum dot solar cells. [ABSTRACT FROM PUBLISHER]

We compare metal oxide semiconductor capacitors, investigating Titanium-Nitride and Molybdenum as gate materials, as well as metal organic chemical vapor deposited ZrO2 and HfO2 as high-κ dielectrics, respectively. The impact of different annealing steps on the electrical characteristics of the various gate stacks is a further issue. The positive effect of post metallization annealing in forming gas atmosphere as well as observed mid-gap pinning of TiN and Mo metal gates is presented. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

High-quality GaN films are prepared by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). In situ optical reflectance traces reveal that the ramping time from low temperature to high temperature in the growth of the nucleation layer significantly affects the surface roughness. Atomic force microscopy (AFM) images demonstrate that the increased ramping time improves the surface roughness and the quality of GaN films. Moreover, the surface roughness also influences the lateral growth and coalescence step. Furthermore, the dependence of the Hall measurement on temperature is investigated. The mobility of the lightly doped GaN is as high as 622 cm2/V-s at a corresponding carrier concentration of 1.1 ×1017 cm-3. The results of this study demonstrate that the proposed GaN films are of high quality and have the excellent electronic property. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

GaN nanorods and 3D columns recently attracted a lot of attention since they are expected to be an exciting new route towards solid state lighting. In contrast to a planar thin film technology, a completely 3-dimensional nanorod approach gives more freedom in the device design. E.g., a core-shell design of LEDs based on 3D GaN offer a dramatically enhanced active area per wafer footprint, since the active area is scaling with height of the 3D structures. High quality core-shell devices will have a tremendous impact on LED technology. [ABSTRACT FROM PUBLISHER]