Tandem GaAsP/SiGe on Si solar cells

Current matched three-terminal dual junction GaAsP/SiGe tandem solar cell on Si

Strained Si/SiGe MOS technology: Improving gate dielectric integrity

This work investigates gate leakage mechanisms in advanced strained Si∕SiGe metal-oxide-semiconductor field-effect transistor (MOSFET) devices. The impact of virtual substrate Ge content, epitaxial material quality, epitaxial layer structure, and device processing on gate oxide leakage characteristics are analyzed in detail. In state of the art MOSFETs, gate oxides are only a few nanometers thick. In order to minimize power consumption, leakage currents through the gate must be controlled. However, modifications to the energy band structure, Ge diffusion due to high temperature processing, and Si∕SiGe material quality may all affect gate oxide leakage in strained Si devices. We show that at high oxide electric fields where gate leakage is dominated by Fowler-Nordheim tunneling, tensile strained Si MOSFETs exhibit lower leakage levels compared with bulk Si devices. This is a direct result of strain-induced splitting of the conduction band states. However, for device operating regimes at lower oxide electri...

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Gate leakage mechanisms in strained Si devices

Material and device analysis of SiGe solar cell in a GaAsP–SiGe dual junction solar cell on Si substrate

Si 1-x Ge x virtual substrates with relaxed graded buffers grown in industrial LPCVD reactors on 150 mm and 200 mm diameter wafers are presented with compositions up to x = 1. By taking advantage of an intermediate planarization step, we are able to achieve dislocation glide limited relaxation throughout the growth of the entire graded buffer layer. This resulted in a threading dislocation density of 2×10 5 cm -2 that was independent of the ultimate composition for substrates with x > 0.4. Ge-on-Si virtual substrates exhibited an rms surface roughness of 3.27 nm for a 20 μm × 20 μm area and a very low density of epitaxial defects. These substrates were used to fabricate both III-V solar cells and visible LEDs. The preliminary results of the devices showed no degradation in device performance from the graded buffer layer, demonstrating the commercial readiness of the SiGe virtual substrates.

Growth and characterization of high-Ge content SiGe virtual substrates

This paper investigates off-state current leakage in strained silicon NMOSFETs built on supercritical thickness strained silicon films. it describes a simple conceptual model for the off-state leakage: the leakage is caused by enhanced dopant diffusion near misfit dislocations. This paper studies the validity of this hypothesis using both DC IV measurements and photon emission microscopy measurements of NMOSFETs with several different supercritical strained silicon thickness values. It shows that the emission measurements of the off-state leakage and the gate length dependence of the off-state leakage can both be easily explained by the leakage model. It also demonstrates that the response to an applied gate or back-bias voltage of the IV characteristics and the light emission data can be understood within the context of the proposed conceptual model.

C. Leitz

Papers

Growth and characterization of high-Ge content SiGe virtual substrates

Investigation of misfit dislocation leakage in supercritical strained silicon MOSFETs

Investigation of electrical properties of furnace grown gate oxide on strained-Si