C.J. Pan

Electrical and optical changes in the near surface of reactively ion etched n-GaN

Abstract Photoluminescence (PL) and ohmic contact resistance measurements were used to characterize the n-GaN surface treated with reactive ion etching (RIE). The n-GaN film was grown on a sapphire substrate by a metal organic chemical vapor deposition process. Subsequently, the GaN film was etched with BCl 3 or Ar gas prior to the PL measurement and contact metal Ti/Al deposition. In PL spectra, we observed the peak shift of the impurity-related emission (yellow luminescence (YL)) for both BCl 3 and Ar etched n-GaN films. The amount of this wavelength shift increases with the RIE rf power increase and depends on the species of the etching gases. The shift of the YL peak decreased after thermal annealing at 500°C for 30 s. The YL peak shift may be attributed to the RIE induced surface point defects. In the ohmic contact resistance measurements, the transmission line model technique was used. The contact resistance of the RIE etched surface is around 5.4×10 −4 Ω cm 2 . However, a lower contact resistance of 5.7×10 −6 Ω cm 2 was obtained for a native surface of n-GaN film. No obvious distinction between the roughness of etched and native GaN surfaces was observed by the atomic force microscope measurements. In an X-ray grazing diffraction measurement, the crystalline lattice orientation and the coherent length of native n-GaN layer were better than the etched n-GaN according to the results of the rocking curve and Θ –2 Θ scan.

The doping of GaN with Mg diffusion

The characteristics of GaN films diAused with Mg were studied. The undoped GaN films were grown by metalorganic chemical vapor deposition (MOCVD). The photoluminescence (PL) spectra of Mg diAused GaN showed a broad violet emission. The Mg-diAused GaN was p-type conductivity with a mobility of 13 cm 2 /V-s and a hole concentration of 3 10 15 /cm 3 at a diAusion temperature of 11008C. However, the samples, which were diAused at 11008C, showed a red emission peak after the annealing process. From the diAusion depth profile observed by secondary ion mass spectrometry (SIMS), we obtained the activation energy of 1.3 eV for Mg diAusion in GaN. # 1999 Published by Elsevier Science Ltd. All rights reserved.

Improvement of near-ultraviolet nitride-based light emitting diodes with mesh indium tin oxide contact layers

The authors have demonstrated nitride-based near-ultraviolet (NUV) light emitting diodes (LEDs) with mesh indium tin oxide (ITO) contact layer. With 20mA injection current, it was found that forward voltages were 3.94 and 4.05V while the output powers were 7.54 and 9.02mW for the planar ITO LED and mesh ITO LED, respectively. The larger LED output power should be attributed partially to the reduced absorption of ITO in the NUV region and partially to the better current spreading.

Dislocation reduction in GaN with multiple MgxNy∕GaN buffer layers by metal organic chemical vapor deposition

Unintentionally doped GaN epitaxial layers with a conventional single low temperature (LT) GaN buffer layer and with multiple MgxNy∕GaN buffer layers were grown on sapphire substrates by metal organic chemical vapor deposition. The multiple MgxNy∕GaN buffer layers exhibit a low nuclei density, increasing the volume of defect-free regions and reducing the dislocations associated with the grain boundaries. Therefore, the GaN with multiple MgxNy∕GaN buffer layers reveals an asymmetrical reflection (102) with a small full width at half maximum, and a higher mobility, lower background concentration, and lower etching pit density than the GaN with the LT GaN buffer layer.

Si diffusion in p-GaN

The characteristics of p-type Mg-doped GaN films diffused with Si are studied. N-type conductivity is achieved, and the carrier mobility of diffused GaN is 90–150 cm2 V−1 s−1, higher than that of p-GaN but less than that of epitaxially grown n-GaN. The Mg acceptor states could become deep compensating defects, and the compensation ratio NA/ND is 0.3, 0.45, 0.6, and 0.75 for 800, 900, 1000, and 1100 °C diffused GaN, respectively. The carrier transport may be dominated by electron hopping through these deep compensating centers or through diffusion. The results of temperature-dependent carrier concentration indicate that thermal annealing may induce defects at the surface, leading to an additional activation energy Ed∼10 meV in the 200–500 K region in diffused GaN.

The doping process of p-type GaN films

Abstract The formation of p-type GaN film is a key technology in developing optoelectronic devices. P-type doping (concentration∼10 17 cm −3 ) has been achieved in grown GaN by metalorganic chemical vapor deposition (MOCVD) with Mg (CP 2 Mg) doping. The Hall measurement results indicate that Mg diffused GaN films also have p-type conductivity with carrier concentration about 10 17 cm −3 and a mobility of 10 cm 2 V −1 s −1 . For the as-grown Mg-doped GaN, the room temperature photoluminescence (PL) spectra show a blue emission peak around 420–450 nm, and the spectral peak depends on the carrier concentrations. For Mg-diffused GaN, the PL spectra shows only a broad violet emission for samples diffused at 900–1100°C.

Microstructure of InN quantum dots grown on AlN buffer layers by metal organic vapor phase epitaxy

InN quantum dots (QDs) were grown over 2in. Si (1 1 1) wafers with a 300nm thick AlN buffer layer by atmospheric-pressure metal organic vapor phase epitaxy. When the growth temperature increased from 450to625°C, the corresponding InN QDs height increased from 16to108nm while the density of the InN QDs decreased from 1.6×109cm−2to3.3×108cm−2. Transmission electron microscopy showed the presence of a 2nm thick wetting layer between the AlN buffer layer and InN QDs. The growth mechanism was determined to be the Stranski–Krastanov mode. The presence of misfit dislocations in the QDs indicated that residual strain was introduced during InN QDs formation. From x-ray diffraction analysis, when the height of the InN QDs increased from 16to62nm, the residual strain in InN QDs reduced from 0.45% to 0.22%. The residual strain remained at 0.22% for larger heights most likely due to plastic relaxation in the QDs. The critical height of the InN QDs for releasing the strain was determined to be 62nm.

Photoluminescence of ZnO Nanowires with Eu Diffusion Process

C. W. Chen, C. J. Pan, P. J. Huang, G. C. Chi, C. Y. Chang, F. Ren, and S. J. Pearton Department of Physics, National Central University, Jhongli, Taoyuan 32001, Taiwan Optical Sciences Center, National Central University, Jhongli, Taoyuan 32001, Taiwan Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA Department of Chemical Engineering, University of Florida, Gainesville, FL 32611, USA

Heteroepitaxial ZnO Films Grown by Plasma-assisted Molecular Beam Epitaxy

Heteroepitaxial ZnO films were grown on GaN templates by plasma-assisted molecular beam epitaxy. The epitaxial GaN templates were deposited by metalorganic chemical vapor deposition on c-plane sapphire substrates. Photoluminescence spectra of ZnO epilayers excited by a He-Cd laser exhibit exciton emission at 376 nm with a full width at half maximum (FWHM) of 10 nm (90 meV) at room temperature. The exciton emission intensity of stoichiometric condition is 2 times greater than that of O-rich and Zn-rich conditions. Samples grown under stoichiometric and Zn-rich conditions do not exhibit defect-related green luminescence, but samples grown under O-rich condition do. In these heteroepitaxial ZnO layers there exists interstitial Zn and Zn vacancies. X-ray diffraction measurements revealed that there exists a residual compressive strain, e~-0.2%, in the [0002] direction of the ZnO epilayer. The residual strain might be attributed to grain boundaries of ZnO.