No abstract

GaN Schottky diodes were exposed to N2 or H2 Inductively Coupled Plasmas prior to deposition of the rectifying contact. Subsequent annealing, wet photochemical etching or (NH&S surface passivation treatments were examined for their effect on diode currentvoltage characteristics. We found that either annealing at 750 'C under N2, or removal of -500-600 A of the surface essentially restored the initial I-V characteristics. There was no measurable improvement in the plasma-exposed diode behavior with (NH&S treatments. 1 DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document.GaN-based devices are being developed for two basic classes of applications, namely blue/green/UV emitters and high power/high temperature electr~nics.(''~) The high bond energy, 8.92 eV/atom, of GaN has necessitated use of dry etching technologies for device patterning. Plasma induced damage to GaN may take several forms, all of which lead to changes in its electrical and optical properties, as follows:1. Ion induced creation of lattice defects which generally behave as deep level states and thus produce compensation, trapping or recombination in the material. Due to channeling of the low energy ions that strike the sample, and rapid diffusion of the defects created, the effects can be measured as deep as 1000 surface, even though the projected range of the ions is only 110 A. to 10l8 cme3. In the PL spectrum an intense broad band appeared at 3.05 eV, and there was an increase in intensity of the yellow band at 2.20 eV. The latter is thought to involve defects such as Ga, in some models. Use of Ar+/N2+ ion beams produced less degradation of both optical and electrical properties.Saotome at studied the effects of RIBEECR etching with pure Cl2 on GaN properties. Etch rates up to -1000 A-min-' at 500 V beam voltage were obtained. He-Cd (325 nm) laser irradiation was used to measure PL from RlBE GaN samples before and after photo-assisted wet etching in an 85% KOH:H20 (1:3) solution. The RIBE treatment decreased near band-edge PL intensity by a factor of approximately five, whereas subs...

The effects of surface treatment using Cl2∕BCl3 and Ar inductive coupled plasmas on the Ohmic characteristics of Ti∕Al∕Ti∕Au contacts to n-type AlxGa1−xN (x=0–0.5) were investigated. Plasma treatment significantly increased the surface conductivity of GaN and Al0.1Ga0.9N, leading to improved Ohmic behaviors of the contacts. However, it reduced the surface doping level in AlxGa1−xN (x⩾0.3) and degraded the contact properties. Following a 900–1000°C anneal, the Ti∕Al∕Ti∕Au contacts to AlxGa1−xN (x=0–0.3) became truly Ohmic, with specific contact resistances of (3–7)×10−5Ωcm2, whereas the contact to Al0.5Ga0.5N remained rectifying even without the plasma treatment. X-ray photoelectron spectroscopy measurements confirmed that the Fermi level moved toward the conduction band in GaN after the plasma treatment, but it was pinned by plasma-induced deep-level states in Al0.5Ga0.5N. This study emphasizes the need to mitigate plasma damage introduced during the mesa etch step for AlGaN-based deep-UV emitters and detectors.

Schottky contacts were formed on n- and p-type GaN after either a conventional surface cleaning step in solvents, HCl and HF or with an additional treatment in (NH4)2S to prevent reformation of the native oxide. Reductions in barrier height were observed with the latter treatment, but there was little change in diode ideality factor. A simple model suggests that an interfacial insulating oxide of thickness 1–2 nm was present after conventional cleaning. This oxide has a strong influence on the contact characteristics on both n- and p-type GaN and appears to be responsible for some of the wide spread in contact properties reported in the literature.

Articles you may be interested inLaser direct writing of GaN-based light-emitting diodes-The suitable laser source for mesa definition