Search

We have investigated the carrier transport mechanism of nonalloyed Ti-based Ohmic contacts to n-AlGaN using current-voltage-temperature and the specific contact resistance-temperature relations. It is shown that the theoretical result obtained using the field emission mode through the shallow-donor-assisted tunneling model is in agreement with the experimental data, although there is a small deviation below 383 K. The deviation is attributed to an increase of the self-compensation between donor-type and acceptorlike defects. This indicates that the electronic transport of the AlGaN contacts is sensitively dependent on Ga and oxygen/nitrogen related surface point defects. [ABSTRACT FROM AUTHOR]

The authors report on the formation of low-resistance and thermally stable Pd/Ni/Pd/Ru Ohmic contacts to Mg-doped AlGaN. The contacts become Ohmic with a contact resistivity of (1.4±0.3)×10-5 Ω cm2 upon annealing at 600 °C for 1 min in a N2 ambient. The samples do not experience significant degradation of the specific contact resistance and the surface roughness even after annealing at 600 °C for 60 min. Based on x-ray photoelectron spectroscopy depth profile results, atomic force microscopy, and contact resistivity-temperature data, possible Ohmic formation and carrier transport mechanisms are described and discussed. [ABSTRACT FROM AUTHOR]

We have demonstrated surface-emitting GaN-based diodes with a buried tunnel junction (TJ) current aperture. The current confinement aperture for lateral injection current was defined by mesa etch of a TJ structure and regrowth of current blocking layer surrounding the TJ mesa. Lateral electron current drives a tunnel contact junction providing hole injection into the active region. The very uniform light emission just through a buried TJ aperture represents that the buried TJ structure acts very effectively as a confinement aperture of lateral current injection, particularly in GaN-based vertical-cavity surface-emitting lasers. [ABSTRACT FROM AUTHOR]

Influence of Mg doping on structural defects in Al[sub 0.13]Ga[sub 0.87]N layers grown on sapphire substrates by metalorganic chemical vapor deposition were studied using transmission electron microscopy. By increasing the Mg source flow rate, the reduction of dislocation density occurred up to the Mg source flow rate of 0.103 μmol/min. While the vertical type inversion domain boundaries (IDBs) were observed in the Al[sub 0.13]Ga[sub 0.87]N layers grown with the low Mg source flow rate, the IDBs in the Al[sub 0.13]Ga[sub 0.87]N layers grown with the high Mg source flow rate have horizontally multifaceted shapes. The change of polarity by the IDBs of horizontal type also resulted in the 180° rotation of pyramidal defects within the same AlGaN layer. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

InGaN/GaN multiple-quantum-well light-emitting-diode structures utilizing tunnel contact junctions grown by metalorganic chemical vapor deposition have been demonstrated. The p[sup +]/n[sup +] GaN tunnel junctions are located in the upper cladding layers of conventional devices, allowing n-type GaN instead of p-type GaN as a top contact layer. Thus, metal ohmic contacts are done at the same time on the top and the lower contact layers. The reverse-biased tunnel contact junction provides lateral current spreading without semitransparent electrode and spatially uniform luminescence exhibiting an improved radiative efficiency. The tunnel contact junction is shown to be an effective method to make possible hole injection via a lateral electron current, with only a small penalty in voltage drop compared to conventional devices. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a selective lateral electrochemical etching using a superlattice as the etch-sacrificial layer. Differing from the previous methods that require a special etch-sacrificial layer and therefore deteriorate the epilayer grown atop, our method simplifies the epi-growth without compromising the epi-quality. At the reverse bias voltage of 20 V in 0.3 M oxalic acid electrolyte, a 50-nm-thick InGaN/AlGaN superlattice was etched laterally at the rate of ∼0.8 μm/min. Our method is efficient enough for the epitaxial lift-off process: an array of 80 μm × 80 μm square platelets is completely detached from substrate, with quantum-well emission properties preserved intact. [ABSTRACT FROM AUTHOR]

The authors have fabricated the surface-textured GaN based light emitting diodes (LEDs) by incorporating a transparent powder onto an indium tin oxide (ITO) surface and exposed n-GaN surface to improve the light extraction efficiency by decreasing the total internal reflection and by achieving an angular randomization of the photons. The ITO surface and exposed n-GaN surface was simultaneously textured using a method known as natural lithography. The Al2O3 powders were coated onto the LED surface as a random mask for dry etching. After packaging, the light output powers of the LEDs with the textured ITO layer and with nanorods at n-GaN were enhanced about ∼ 11 and 15 %, respectively, compared with that of the conventional LED. Also, the light output power of the LED with both the textured ITO layer and the formed n-GaN nanorods increased by ∼ 24% compared with that of the conventional LED. [ABSTRACT FROM AUTHOR]