J. T. Hsieh

Surface etching of InP(100) by chlorine

The cleaning and etching of the InP(100) surface by chlorine gas is investigated using synchrotron-radiation photoemission spectroscopy. A clean InP surface with a 4◊2 configuration is obtained by ion sputtering or chlorine etching, followed by annealing to 650 K. The clean surface obtained by chlorine etching and annealing is indium-rich with the surface indium atoms showing metallic characterics. The chemisorption of chlorine leads to the formation of various InCl x (x=1‐3) and PCl species on the InP surface at 110 K and their corresponding chemical shifts are assigned. The chlorination of the InP surface causes surface band bending by about 0.36 eV at the saturation coverage. Argon-ion sputtering enhances the surface reactivity so that the sputtered surface can be chlorinated to a higher extent than the clean surface.

Defect depth profiling using photoluminescence and cathodoluminescence spectroscopy : the role of oxygen on reactive ion beam etching of GaN in O2/Ar plasmas

Abstract This work investigates reactive ion beam etching processes of GaN in O 2 /Ar plasmas and examines the electrical behavior of Schottky diodes fabricated on O 2 /Ar plasmas reactive ion beam (RIB) etched samples. To explore the role that the oxygen plasma plays on the etched GaN, photoluminescence and depth-resolved cathodoluminescence are applied to elucidate the defect relative yellow luminescence. The observation of oxygen-content-dependent defects that are associated with the yellow band has important consequences for our understanding of defect-related luminescence in GaN.

Photoelectrochemical etching of InxGa1−xN

Photoelectrochemical (PEC) etching of InxGa1−xN in the KOH solution under illumination of a Hg-arc lamp is studied. An indium oxide surface layer is formed during PEC etching, which slows down the etching rate. The PEC etch rate of InxGa1−xN is determined by dissolution of indium oxides into the solution. Increase of the solution temperature results in an increase of solubility of indium oxides and thus enhances the PEC etch rate. It is found that stirring the solution can accelerate indium oxides to dissolve into the solution and increase the etch rate. The thick indium oxide layer on the PEC-etched InxGa1−xN surface can be effectively removed by the treatment of using a hot 6N HCl solution. A post-treatment by using a 3.2 M KOH solution can provide a smooth sidewall on the PEC-etched surface for the potential application to laser cavity.

Effect of Ar ion beam channeling on AlGaN/GaN heterostructures during the ion beam etching process

The effect of Ar+ ion beam etching of AlGaN/GaN heterostructures at a bias voltage of 250 V was investigated with respect to different ion incident angles. The samples were measured before and after etching with respect to mobility, sheet electron concentration, and sheet resistance. We found a pronounced dependency of the electrical characteristics after etching on the ion incident angle. Especially at zero degree, the mobility of the two-dimensional electron gas (2DEG), which is located at the AlGaN/GaN interface, decreases dramatically after etching. The sheet resistance increases in the same way. At larger ion incidence angles, the effect vanished. We attribute this behavior predominantly to channeling of the ions through the AlGaN layer down to the 2DEG. An annealing step after etching shows improvement of the electrical characteristic. These results show that gate-recessed GaN field effect transistors can be limited in their device performance by etch-process-induced ion channeling effects. The resu...

Photoluminescence Study on Threading Dislocation in GaN Revealed by Selective Photoelectrochemical Etching

Selective etching was studied between the crystalline GaN and its dislocations by controlling the KOH concentration and the ult raviolet photon intensity in photoelectrochemical (PEC) etching. The PEC etching rate of GaN is governed by the density of photogenerated carriers and the direct chemical reaction between GaN and the electrolyte. The dislocation is more chemically reactiv e than crystalline GaN, whereas crystalline GaN has a higher density of the photogenerated minority carrier than the threading dis location. By using the selective etching method, the origin of photoluminescence (PL) from the near bandedge of crystalline GaN and dislocations could be clarified. The room-temperature PL peak at 3.41 eV is due to the emission from the crystalline GaN an d the peak at 3.35 eV is attributed to the threading dislocation.

Damage-Free Photo-Assisted Cryogenic Etching of GaN as Evidenced by Reduction of Yellow Luminescence

Damage-free etching of GaN by Cl 2 , assisted by an ArF (193 nrm) excimer laser, is demonstrated. At low temperatures, photo-assisted etching can provide a better etch rate and largely improve the surface morphology and quality. AFM results show that the etched GaN surface is obtained with a root-mean-square roughness of 1.7 nm. As compared with the photoluminescence spectra of photoelectrochemical wet etched GaN, the photo-assisted cryogenic etching is proved to be a damage-free dry etching technique.