Ge Si Substrate Research Articles

In0.3Ga0.7As heterojunction bipolar transistor grown on GeSi substrate for high-frequency application

We report an In0.3Ga0.7As HBT device grown on a 200 mm Si wafer using GeSi as virtual starting substrate and InAlAs as the compositionally graded buffer layer from GaAs to In0.3Ga0.7As lattice constant. A DC gain, emitter-base, and base-collector ideality factors of 10, 1.43, and 1.56, respectively, are obtained for a device with an emitter area of 40 × 50 μm2. Small-signal simulation of an In0.3Ga0.7As HBT device with 2 × 8 μm2 emitter area shows that current gain cutoff frequency (fT) and maximum cut-off frequency (fMax), of 50 GHz and 220 GHz, respectively, can be achieved with base doping and layer thickness of 2 × 1018cm−3 and 30 nm, respectively.

Direct MBE growth of metamorphic nBn infrared photodetectors on 150 mm Ge-Si substrates for heterogeneous integration

GaSb-based infrared (IR) photodetector structures were grown on large diameter, 150 mm, Si substrates using a multistep metamorphic buffer architecture process. A standard bulk InAsSb/AlAsSb barrier detector design with a cutoff wavelength of ∼4 μm was used as a test vehicle for this growth process. First, a Ge layer was deposited by chemical vapor deposition, creating a Ge-Si substrate for the subsequent molecular beam epitaxy growth of the remaining III–V buffer and device layers. X-ray diffraction and photoluminescence measurements demonstrated high crystal quality and excellent cross-wafer uniformity of the device epiwafer characteristics. Microscopy evaluation revealed a moundlike surface morphology with a low root-mean-square roughness value below 2 nm, suitable for focal plane array (FPA) fabrication. Large-area mesa diode test devices measured dark currents of 5 × 10−5 A/cm2 and a quantum efficiency of 60% for the Sb-detector grown on Ge–Si. The same structure was fully fabricated into a standard FPA and produced good imagery resolution with high operability. These excellent results for this first FPA manufactured from an Sb-photodetector grown on Si using this Ge-Si architecture demonstrate a promising path in the progression of Sb-IR technology as it transitions from development to next-generation, large-format IR manufacturing with an eye toward potential heterogeneous integration with silicon.

Room Temperature 3.5-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math> </inline-formula> Mid-Infrared InAs Photovoltaic Detector on a Si Substrate

We report a mid-infrared InAs p-i-n photovoltaic detector on a Si substrate operating at room temperature with a cutoff wavelength at 3.5 $\mu \text{m}$ . The large 11.6% lattice mismatch between the device layer (InAs) and the Si substrate is accommodated by employing a compositionally graded buffer layer technique using solid-source molecular beam epitaxy and a commercially available GeSi substrate. An Al x In1– x As graded buffer layer is used to linearly scale the lattice constant from AlAs to InAs with an increasing $x$ value. The photovoltaic detector has a responsivity of 0.57 A/W, measured using a blackbody source maintained at 700 °C.

Near-edge conduction band electronic states in SiGe alloys

Spatially resolved electron energy loss spectroscopy (EELS) measurements in GeSi alloys illustrate the relationship of atomic structure to local electronic structure. Extending earlier measurements, where electronic structure was found to be controlled by composition in relaxed alloys, measurements in anisotropically strained alloys show splitting of normally degenerate band edges into two components. In a strained Si quantum well, this allows the engineered band offset to be followed from the GeSi substrate through the well to the alloy-capping layer. In the high-mobility conduction channel, the band edge is found to be very sharp, in spite of obvious composition roughness. Near a misfit dislocation under the Si well, the band edge can shift by as much as 0.25 eV due to local strain. Within the core of the defect, however, strictly local behavior dominates the observations. Local conduction band splitting and in-gap states are both observed.

Melting and diffusion under nanosecond laser pulse

A computer simulation study of the melting process in Si, Ge and Sb under an UV laser beam was performed by means of the Finite Element Method (FEM). The melting threshold and melt duration of Si, Ge and Sb crystals were determined and a very good agreement with the Real Time Reflectivity (RTR) measurements is presented. Sb Ge-Si substrate multilayer systems are also studied. The simulated melt duration was lifted to the experimental data assuming 400 K undercooling of the molten layer prior to the solidification. Ge diffusion in the sample is also presented and the diffusion constant D = 7.5 × 10 −5cm 2/s was determined.

Growth of a GeSi thick alloy layer on a Si substrate by liquid phase epitaxy

A novel technique termed the “yo-yo solute feeding method”, for the preparation of either a thick layer of a GeSi alloy or a GeSi substrate is described. In this method, a Sn-Ge-Si solution was “sandwiched” between two sheets of a Si(111) crystal to form a double crystal system, and the temperature was periodically modulated with an amplitude of 10 to 20° C within the temperature range of 910 to 980° C to produce what has been termed a “yo-yo” cycle. A Ge0.24Si0.76 alloy layer about 0.8 mm thick was successfully grown on the bottom surface of the upper silicon(111) crystal. When a third Si sheet crystal was inserted between the two Si crystals to form a triple crystal system, epitaxial growth occurred on the bottom surface of the middle crystal and this was accompanied by meltback on the top surface. The implication of this result is that it may be possible to transform the entire middle Si crystal into a GeSi alloy following the application of numerous “yo-yo” cycles.