A low-energy argon sputter process has been optimized to successfully remove native oxide from a silicon surface at elevated temperatures without introducing permanent damage. The process relies upon confining all sputtering events to the near-surface region of the silicon and exploits the enhancement of sputter efficiencies observed for silicon and silicon dioxide above 600 °C. The procedure has been implemented as an in situ etch for low-temperature (below 800 °C), very low-pressure (1–10 mTorr), epitaxial silicon deposition in a high vacuum ambient. The reactor and conditions employed are presented along with measures of residual substrate damage as a function of processing conditions, and the process limitations are discussed. A companion paper describes the excellent structural quality of the resultant epitaxial films. The ion energies (100 eV) and fluxes (5×1013 cm−2 s−1) employed represent a significant departure from conventional sputter cleaning processes.
Quantum scattering and adiabatic channel treatment of the low-energy and low-temperature capture of a rotating quadrupolar molecule by an ion J. Chem. Phys. 120, 9989 (2004); 10.1063/1.1724822Electrical quality of lowtemperature (T dep=775°C) epitaxial silicon: The effect of deposition rate Electrical quality of lowtemperature (T dep≤800°C) epitaxial silicon: The effect of deposition temperature Silicon surface cleaning by low dose argonion bombardment for lowtemperature (750°C) epitaxial silicon deposition. I. Process considerations Argon-ion bombardment has been optimized as a method to clean silicon substrates prior to epitaxial deposition at low temperatures (750 ·C) and very low pressures ( < 1 X 10-2 Torr).Structural characterization of subsequently deposited films has been performed to establish the relations between cleaning conditions and film properties. When cleaning conditions are insufficient, a residue of native oxide remains at the interface and disrupts the transfer of crystalline structure from the substrate to the epitaxial layer. When cleaning conditions are excessive, the substrate is damaged and the initial stages offilm nucleation and growth are disrupted. Using an elevated substrate temperature of 750 ·C, a window in ion energy and dose has been found in which native oxide is removed without net damage being produced in the substrate. Under these conditions, epitaxial films of excellent structural. quality may be deposited, as evidence by transmission electron microscopy and defect etching.3398
Thermophotovoltaic (TPV) converters were developed and tested at the heat source operating temperature of 1700 K. Rare-earth-doped yttrium aluminum garnet (YAG) and lutetium yttrium aluminum garnet (Lu,YAG) selective emitters, as well as a blackbody emitter, were coupled to InGaAdInP photovoltaic (PV) cells and bandpasslinfrared (IR) reflector filters. YAG-based selective emitters were doped with Ho, Tm, and Er. PV cells had bandgaps of 0.51, 0.57, and 0.69 eV. Converter energy conversion efficiencies approaching 30%, as well as electrical output power densities near 2 W/cm2 were demonstrated.The overall performance of the filtered blackbody-based converter was found to be superior to the selective emitter YAG-based converters. The details of the measurements performed on the above converters and their individual components are presented.
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