RHEED patterns taken along GaN direction from the surfaces of epitaxial GaN-on-Si(111) at nominal thicknesses of (a) 5 BLs and (b) 20 BLs. Panels (ii) and (iii) refer to growth at temperatures of 400 and 650 °C, respectively, while the RHEED pattern (i) is from Si(111)−(7 × 7) substrate surface.
RHEED patterns along GaN of epitaxial GaN-on-Si(111) but at thicknesses of (a) 90 BLs and (b) 630 BLs. Panels (i) and (ii) are for films grown at 400 and 650 °C, respectively. (ic) and (iic) are SEM micrographs showing the surfaces of ∼200 nm thick GaN films grown on Si(111) at 400 and 650 °C, respectively. The insets show the same surfaces with higher magnification.
(Color online) RHEED patterns along GaN of epitaxial GaN films deposited on Si(111) at 650 °C (HT) but with a ∼6.6 nm thick GaN buffer deposited at 400 °C (LT) underneath. The HT-film thickness for (a), (b), and (c) are 3, 36, and 250 nm, respectively. Panel (d) shows the (average) intensity profile taken along lines in the region illustrated by the dashed box in (b), from which the values of D and W are measured.
(Color online) (a) Evolution of the RHEED pattern width (W) as a function of HT-film thickness. Different curves show results for different LT-buffer thickness. The evolutions of in-plane lattice constant as derived from D are also shown, comparing that of strain-free Si and GaN (dash-dotted lines). (b) FWHM of the XRD rocking curve (RC) of GaN(0002) diffraction for ∼250 nm thick GaN films grown at 650 °C but having different LT-buffer thicknesses. The inset shows the original XRD curves, and the SEM micrographs are for samples indicated by arrows.
TEM micrographs (zone axis: Si) of GaN-on-Si(111) samples grown at 650 °C without (a, b) and with (c, d) a ∼6.6 nm thick LT-buffer. The high resolution images of (a) and (c) reveal the presence of amorphous-like interface layers, while in (b) and (d), threading defects in epifilms are revealed. The inset in (d) shows the selective area diffraction pattern of the sample.
(Color online) (a) Room-temperature I−V characteristics of heterojunctions of (i) GaN/p-Si (Al electrodes) and (ii) GaN/n −-Si (ITO and Ag electrodes for GaN and n −-Si, respectively). The inset shows, in a semi-logarithm plot, the forward-bias I−V data obtained at different temperatures between 18 and 400 K. (b) Current-temperature (I−T) dependence at different forward-bias conditions. The inset shows the same data in an Arrhenius plot.
Article metrics loading...
Full text loading...