Papers by Keyword: Silicon Germanium

Abstract: Advanced technology node demands new capabilities in pre-cleaning substrates of epitaxy films. In particular, cleaning carbon and native oxide on Si and SiGe surfaces are required. In this paper, we present an approach to cleaning both carbon and Si/SiGe native oxide using Previum chamber with two distinct chemistries. FTIR and SEM are used to characterize the conversion and sublimation steps of cleaning native oxide, and carbon film etch rate by hydrogen radicals is presented. The carbon cleaning and oxide cleaning capabilities are integrated in Previum chamber and significantly improved cleaning results are supported by SIMS.

Abstract: This paper presents the performance between silicon germanium (SiGe) and crystalline germanium (Ge) solar cells in terms of their simulated open circuit voltage, short circuit current density, fill factor and efficiency. The PC1D solar cell modeling software has been used to simulate and analyze the performance for both solar cells, and the total thickness is limited to 1μm of both SiGe and Ge solar cells. The Si_0.1Ge_0.9 thickness is varied from 10nm to 100nm to examine the effect of Si_0.1Ge_0.9 thickness on SiGe solar cell. The result of simulation exhibits the SiGe solar cell give a better performance compared to Ge solar cell. The efficiency of 9.74% (V_OC = 0.48V, J_SC = 27.86mA/cm², FF =0.73) is achieved with Si_0.1Ge_0.9 layer of 0.1μm in thickness whilst 2.73% (V_OC = 0.20V, J_SC = 27.31mA/cm², FF =0.50) efficiency is obtained from Ge solar cell.

Abstract: In this paper, we propose a novel material- amorphous silicon germanium(a-SiGe). The a-SiGe film was formed by PECVD at a low temperature and a low frequency. By adjusting the fraction x of Ge in Si_1-xGe_x, optimal SiGe bandgap was achieved. We used amorphous silicon germanium alloy as MOSFET source/drain. The parameter of MOSFET shows that, as the fraction increases, the drain-to-source breakdown voltage increases. With reduction of the minority carrier inject ratio, the current gain β of parasitic BJT in MOSFET was reduced greatly, which eliminates the limit of the breakdown voltage of the device.

Abstract: The results of the experimental studies of the effect of nanoislands on the lateral photoconductivity in structures with Ge nanoislands formed on the SiOx layer using molecular beam epitaxy are reported. It is shown that nanoislands increase the surface recombination rate and affect the fundamental absorption edge of c-Si. The generation of lateral photocurrent in the range 0.8 – 1.0 eV was observed due to transitions between tails in the density of states of the near-surface c-Si, which is described by Urbach dependence. It was shown that the absorption spectrum of nanoislands is typical for the disordered Ge and is due to transitions between density-of-states tails of the valence and conductance bands. The mechanism is proposed of lateral photoconductivity involving the non-equilibrium charge carriers, generated in Ge nanoislands. It is suggested that the optical absorption and lateral photocurrent in Ge-SiOx-Si structures are affected by fluctuations of the surface potential in the near-surface region of c-Si, fluctuations of the Si band gap width and by effects of disorder in Ge nanoislands.

Abstract: Terahertz-range photoluminescence from silicon-germanium crystals and superlattices doped by phosphor has been studied under optical excitation by radiation from a mid-infrared CO2 laser at low temperature. SiGe crystals with a Ge content between 0.9 and 6.5 %, doped by phosphor with a concentration optimal for silicon laser operation, do not exhibit terahertz gain. On the contrary, terahertz-range gain of ~ 2.3 - 3.2 cm-1 has been observed for donor-related optical transitions in Si/SiGe strained superlattices at pump intensities above 100 kW/cm2.

Abstract: Molecular beam epitaxy is employed for the growth of strained-Si layers on top of virtual substrates with highly-relaxed ultrathin SiGe buffers in a continuous procedure. An initial growth stage at a temperature-ramp down to below 200°C causes misfit-dislocation generation by nucleation from point defects and provides an early relaxation in the SiGe buffers. In situ monitoring is used for the growth control. Layer thicknesses and composition are proved by ex situ spectroscopic ellipsometry. %Raman investigations on the layer stacks reveal high degrees of relaxation (70-100%) in sub-100nm SiGe buffer layers containing from 12 to 42 % Ge. Stress in strained Si layers estimated by means of Raman-spectra shift is adjustable from 0.92 to 6.84 GPa by the Ge-content in virtual substrates. Surface morphology of strained Si and of relaxed SiGe buffers is smooth and crosshatch-free. Device test structures show substantial increase of carrier mobilities in nMOSFETs fabricated on these strained-Si layers.