Gallium nitride surface preparation optimised using in situ scanning tunnelling microscopy

Atomic-scale studies on the growth of palladium and titanium on GaN(0001)

“…In situ cleaning involved either a 20 min anneal in an ammonia atmosphere (2 · 10 À5 Pa) or heating in UHV up to about 700°C to remove the surface oxide and produce Ga-rich GaN(0 0 0 1) surfaces with variable amounts of excess gallium. The detailed cleaning procedures and the resulting GaN(0 0 0 1) surface structures have been described elsewhere [10]. Temperatures were measured using an infra-red pyrometer with an accuracy of ±20°C.…”

“…Systematic control of the deposition conditions as well as the effective preparation of clean GaN surfaces is therefore crucial for the performance of the contacts. In a previous study, we have identified the effect of different surface cleaning treatments on surface reconstruction, morphology and stoichiometry of the GaN(0 0 0 1) surface [10], whereas, other authors have investigated the effect of specific surface treatments on the electrical properties of ohmic contacts to both n-type and p-type GaN [1,2,11,12]. Here, we have focused on atomic-scale studies of the initial growth stages of palladium and titanium on the GaN(0 0 0 1) surface depending on deposition conditions and substrate stoichiometry using in situ elevated-temperature STM.…”

High-fluence hyperthermal ion irradiation of gallium nitride surfaces at elevated temperatures

“…Some groups performed molecular dynamic simulations to determine threshold energies for ion impact induced lattice displacements of gallium and nitrogen atoms [17,18] as well as energy thresholds for sputtering [19,20,25]. Most of the studies were performed with argon ions [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] but there are rarely investigations using nitrogen ions [31][32][33][34][35][36][37][38]. As can be derived from Table 1, no ion irradiation experiments of GaN were performed in the hyperthermal nitrogen ion energy regime <60 eV.…”

Scanning probe microscopy studies on the growth of palladium and nickel on GaN(0001)

“…Insitu cleaning involved either a 20 min anneal in an NH 3 atmosphere (2×10 -5 Pa) or careful heating in UHV up to about 700 ºC to remove the surface oxide and produce Ga-rich GaN (0001) surfaces. The detailed cleaning procedures and the resulting GaN(0001) surface structures have been described elsewhere [7]. The growth experiments were carried out in the STM chamber of a JEOL 4500XT UHV STM.…”

“…Control of the metal deposition conditions as well as the effective preparation of clean GaN surfaces is therefore crucial for the performance of the contacts. In a previous study, we have identified the effect of different surface treatments on surface morphology and stoichiometry of the GaN(0001) surface [7], whereas other authors have investigated the effect of specific surface treatments on the electrical properties of ohmic contacts to n-and p-type GaN [1,8,9].Here, we have focused on atomic-scale studies of the initial stages of growth of palladium and nickel on the GaN(0001) surface using in-situ variable-temperature STM. Complementary meso-scale tapping-mode AFM imaging was carried out in order to characterize the density and distribution of structures as a function of processing parameters.…”