Deposition of Gallium Nitride Films using Ammonia and Triethylgallium Seeded Helium Beams
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Figure 1. Seeded beam deposition system. Table I. Typical experimental conditions/ system capabilities. Value 8 x 10-7 Torr 5 x 10-4 Torr 5% volume 800 Torr 12/240 sccm 150 gtm 550 0 C -100 C 860 Torr 40 sccm He 20 gtm 0.034 sccm 354:1 600 0C
System parameter Base vacuum Pressure during deposition NH 3 seeding percentage NH 3 jet stagnation pressure NH3/He flow rates during deposition NH3 orifice diameter NH 3 orifice temperature TEGa bubbler temperatures TEGa stagnation pressure TEGa carrier TEGa orifice diameter TEGa delivery rate NH 3 :TEGa ratio Substrate temperature Sample cleaning! preparation
A120 3 (0001) samples were prepared in a three step cleaning process: 10 minutes in a trichloroethylene containing ultrasonic bath, 15 minutes in an 80'C acid bath containing a 50:50 mixture of H3 PO 4 and H 2SO 4 , 5 minutes in 10% HF solution. Si(100) samples were immersed in a 10% HF solution for 5 minutes and subsequently exposed to an ultraviolet light: air oxidation step after which the samples were immersed in a separate 10% HF solution for 5 minutes. Both A12 0 3 (0001) and Si(100) substrates were blown dry with LN 2 boil-off immediately before mounting on travelers and installation into the reactor. Auger analysis Auger electron spectroscopy was performed in a 10-10 Torr base pressure ultrahigh vacuum analysis system with a Physical Electronics 10-155 cylindrical-Auger Electron optics detector with a coaxial electron gun operated by a Physical Electronics 11-010 electron gun controller. The Auger optics were supported by a Physical Electronics 32-100 electron multiplier module. 332
Samples were Ar ion sputtered in-situ prior to Auger examination. Auger measurements were performed with a primary electron energy of 3 keV and data was collected for 10 ms at each I eV scanning step for 15 iterations. Reflection high energy electron diffraction Electron diffraction characterization of deposited films was performed with a Physical Electronics electron gun operated at 10 keV by a 20-330 analog HEED gun controller. The electron source was 12" from the sample center and the screen was also 12" from the sample center. Scanning electron microscopy A JEOL 6400 field emission scanning electron microscope (SEM) operated with a 5 keV primary beam was used for the SEM images in this report. For the cross sectional images, the samples were cleaved immediately before installation in the SEM. RESULTS Single step deposition A series of experiments was performed to study the effect of the NH 3 :TEGa supply ratio on the properties of resulting films. By varying the TEGa bubbler temperature while holding all flow rates and pressures constant, it was possible to explore this ratio effect without the added complication of gas flow pattern changes. Three samples were prepared and examined via SEM and Auger chemical spectroscopy. The NH 3 :TEGa ratio achieved at each bubbler temperature used is presented in Table II. Figure 2 displays the Auger spectra collected f
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