Deep centers in a free-standing GaN layer

Abstract

Schottky barrier diodes, on both Ga and N faces of a ∼300-μm-thick free-standing GaN layer, grown by hydride vapor phase epitaxy (HVPE) on Al2O3 followed by laser separation, were studied by capacitance–voltage and deep level transient spectroscopy (DLTS) measurements. From a 1/C2 vs V analysis, the barrier heights of Ni/Au Schottky contacts were determined to be different for the two polar faces: 1.27 eV for the Ga face, and 0.75 eV for the N face. In addition to the four common DLTS traps observed previously in other epitaxial GaN including HVPE-grown GaN a new trap B′ with activation energy ET=0.53 eV was found in the Ga-face sample. Also, trap E1 (ET=0.18 eV), believed to be related to the N vacancy, was found in the N-face sample, and trap C (ET=0.35 eV) was in the Ga-face sample. Trap C may have arisen from reactive-ion-etching damage.

Characterization of free-standing hydride vapor phase epitaxy GaN

“…The polarity determination by CBED is consistent with chemical etching experiments in which the Nface etched very rapidly in hot phosphoric acid (H 3 PO 4 ). In addition, Schottky barriers fabricated on this surface exhibited a much reduced Schottky barrier height (0.75 eV vs. 1.27 eV on the Ga-face), only after some 30-40 µm of the material was removed by mechanical polishing followed by chemical etching to remove the damage caused by the first mechanical polish 16 .…”

Characterization of near-surface traps in semiconductors: GaN

“…Although we do not yet know the origin of trap C, it is probably defect-related, because, e.g., it seems to be generated during ion-beam etching 11 and sputtering. 13 Such processes would be expected to produce damage only up to a few 1000 Å, 14 as observed here.…”

“…Recent optical, 7-9 electrical, 7,8,10,11 and structural 8,9 measurements, including DLTS, 11 have demonstrated the excellent quality of such material; e.g., one wafer has exhibited the highest GaN mobility ever measured ͑ϳ1200 cm 2 /V s at 300 K͒, and the lowest donor and acceptor concentrations, about 8ϫ10 15 and 3ϫ10 15 cm Ϫ3 , respectively. 10 However, the particular wafer studied here had N D net ϭ1ϫ10 16 cm Ϫ3 , from C -V measurements on the same Schottky-barrier diode ͑SBD͒ as that used for DLTS.…”

“…The previous DLTS study of this material 11 identified five common traps on Ga-face SBDs, with energies as follows: A 1 (1.04 eV͒, A͑0.66 eV͒, B͑0.59 eV͒, C͑0.34 eV͒, and D͑0.24 eV͒. ͑However, that study 11 did not determine concentrations accurately, because the ␦ effect was not taken into account͒. Each of these traps has been seen in earlier DLTS studies of GaN grown by various epitaxial techniques or subjected to certain types of processing.…”

“…The analysis developed here is used to establish the bulk or near-surface nature of traps in a recently introduced form of GaN grown by hydride vapor phase epitaxy ͑HVPE͒. [7][8][9][10][11] The capacitative DLTS experiment is based on observing a change in capacitance ⌬C as a result of a forward-bias pulse which fills traps and thus changes their charge states.…”