Influence of active nitrogen species on high temperature limitations for (0001_) GaN growth by rf plasma-assisted molecular beam epitaxy

Abstract

High temperature limitations for GaN growth by rf-plasma assisted molecular beam epitaxy: Effects of active nitrogen species, surface polarity, hydrogen, and excess Ga-overpressure J.The relation of active nitrogen species to high-temperature limitations for (0001) GaN growth by radio-frequencyplasma-assisted molecular beam epitaxy A reduced growth rate for plasma-assisted molecular beam epitaxy GaN growth often limits growth to temperatures less than 750°C. The growth rate reduction is significantly larger than expected based on thermal decomposition. Characterization of various rf plasma source configurations indicated that a flux consisting predominantly of either atomic nitrogen or nitrogen metastables can be produced. The use of atomic nitrogen, possibly coupled with the presence of low energy ions, is associated with the premature decrease in growth rate. When the active nitrogen flux consists primarily of nitrogen metastables, the temperature dependence of the decrease is more consistent with decomposition rates. A significant improvement in electrical properties is observed for growth with molecular nitrogen metastables. In addition, atomic hydrogen stabilizes the growing surface of (0001 គ ) GaN.

Absolute densities of N and excited N2 in a N2 plasma

“…Several studies in the deposition of GaN using N 2 plasmas have revealed that the properties of the deposited thin films depend on the relative flux of N and excited N 2 (N 2 *) to the surface during growth. [7][8][9] Specifically, N 2 * is thought to be more desirable for GaN growth since it facilitates higher film growth rates at lower substrate temperatures with significantly improved electrical properties in comparison to growth with a predominantly atomic N flux. 7,8 Thus, there is a need to simultaneously characterize the N and N 2 * fluxes impinging on the substrate to determine the role of these precursors during deposition.…”

“…[7][8][9] Specifically, N 2 * is thought to be more desirable for GaN growth since it facilitates higher film growth rates at lower substrate temperatures with significantly improved electrical properties in comparison to growth with a predominantly atomic N flux. 7,8 Thus, there is a need to simultaneously characterize the N and N 2 * fluxes impinging on the substrate to determine the role of these precursors during deposition. In this letter, we report the use of modulatedbeam line-of-sight threshold ionization mass spectrometry ͑LOS-TIMS͒ to measure the absolute densities of N and N 2 * in an N 2 plasma.…”

High temperature limitations for GaN growth by RF‐plasma assisted molecular beam epitaxy: Effects of active nitrogen species, surface polarity, and excess Ga‐overpressure

“…Two rf-plasma sources were used to produce active nitrogen, an Oxford Applied Research CARS-25 (Oxfordshire, UK) and a Veeco Instruments Inc. (formerly Applied EPI) (St. Paul, MN) Unibulb source. Characterization of these sources has been extensively reported elsewhere [1][2][3][4]. The Oxford source produced primarily atomic nitrogen as the active species under our operating conditions, while the EPI source produced primarily metastable molecular nitrogen corresponding to the A u 3 Σ + metastable state [5,6] with a significant atomic nitrogen component remaining.…”

Control of nitrogen flux for growth of cubic GaN on 3C-SiC/Si by RF-MBE

“…Vaudo et al also studied the two type plasma sources [7,8] and showed details of the atomic N emission lines [8]. Myers et al compared several RF plasma cells such as an Oxford Applied Research source and an EPI Vacuum Unibulb source [9]. They showed that the smaller size of hole diameter, or aperture, of an orifice reduced the ion flux and increased the contribution from atomic N. The high efficiency of the production of atomic N could be realized at higher pressure with the small holes.…”