Properties of radio-frequency-sputter-deposited GaN films in a nitrogen∕hydrogen mixed gas

Abstract

GaN films have been deposited by reactive sputtering in nitrogen gas at pressures from 0.08 to 2.70 Pa with and without the addition of hydrogen gas. X-ray diffraction (XRD), Fourier transform infrared (FTIR), optical absorption, and photoluminescence (PL) spectroscopy have been used to characterize the sputter-deposited GaN films. The XRD pattern reveals that the GaN films deposited in nitrogen gas at pressures lower than 0.53 Pa are polycrystals with the (0001) texture (α-GaN), while those deposited at or above 1.07 Pa display mixed crystalline orientations or an amorphous-like nature. The GaN:H films deposited in nitrogen∕hydrogen mixed gas, on the other hand, show an amorphous or amorphous-like nature. The FTIR spectra indicate that the GaN:H films show peaks arising from hydrogen-related bonds at ∼1000 and ∼3200cm−1, in addition to the GaN absorption band at ∼555cm−1. The optical absorption spectra at 300 K indicate the fundamental absorption edges at ∼3.38 and ∼3.7eV for the highly oriented α-GaN and amorphous GaN:H films, respectively. PL emission has been observed from sputter-deposited α-GaN films at temperatures below 100 K. The GaN:H films also show strong band-edge and donor-acceptor pair emissions. The PL emission in the GaN:H film may arise from crystalline GaN particles embedded in the amorphous GaN matrix.

Improved optical and electrical properties of low-temperature sputtered GaN by hydrogenation

“…In the range of 1.95-2.30 eV, the hydrogenated sample exhibits luminescence in a broad band, consisting of two overlapping peaks centered at 1.99 and 2.13 eV. The trends in the PL intensity are different from those observed by Miyazaki et al 8 There, PL was only observed below 100 K without hydrogenation and in a broad band at 1.9-3.3 eV. Hydrogenation gave rise to a single room-temperature luminescence peak at 3.25 eV.…”

“…Miyazaki et al observed that films sputtered with H 2 become amorphouslike. 8 The surfaces of the 100 nm films become increasingly rough with H 2 flow, but there is nothing obvious to explain the resistivity minimum at 2.4% H 2 .…”

“…[7][8][9] Hydrogen is thought to passivate dangling bonds, dislocations, and defects in amorphous and polycrystalline materials, just as it does in a-Si: H. Hydrogenation of GaN during growth by remote-plasma metal-organic chemical-vapor deposition at 380°C has made it possible to fabricate visible-blind photodiodes 10 and light-emitting devices. 11 The addition of H 2 during the growth of both single-crystal 9 and disordered materials 8 has been observed to increase the intensity of the photoluminescence ͑PL͒ significantly. In the latter case, the material was grown in a similar manner to that reported here, but using magnetron sputtering and no Ar, and the optical properties were examined.…”

Nanocrystalline GaN and GaN: H films grown by RF-magnetron sputtering

“…Several reports are found for different material structures: single crystal [2][3][4], nanocrystalline [5,6], and amorphous [7]. Most studies refer to film preparation onto different substrates due to the difficulties concerning the growth of GaN bulk crystals [2][3][4].…”

“…The effect of hydrogenation/de-hydrogenation of GaN was analyzed by several authors, but the analysis are almost [6] completely restricted to the passivation of defects and impurities in single crystal GaN films [9,10].…”