This article reviews the history and current progress in high-mobility strained Si, SiGe, and Ge channel metal-oxide-semiconductor field-effect transistors (MOSFETs). We start by providing a chronological overview of important milestones and discoveries that have allowed heterostructures grown on Si substrates to transition from purely academic research in the 1980’s and 1990’s to the commercial development that is taking place today. We next provide a topical review of the various types of strain-engineered MOSFETs that can be integrated onto relaxed Si1−xGex, including surface-channel strained Si n- and p-MOSFETs, as well as double-heterostructure MOSFETs which combine a strained Si surface channel with a Ge-rich buried channel. In all cases, we will focus on the connections between layer structure, band structure, and MOS mobility characteristics. Although the surface and starting substrate are composed of pure Si, the use of strained Si still creates new challenges, and we shall also review the literature on short-channel device performance and process integration of strained Si. The review concludes with a global summary of the mobility enhancements available in the SiGe materials system and a discussion of implications for future technology generations.

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We report a study on Ge diffusion and its impact on the electrical properties of TaN∕HfO2∕Ge metal-oxide-semiconductor (MOS) device. It is found that Ge diffusion depends on the amount of GeO2 formed at the HfO2∕Ge interface and can be retarded by surface nitridation. It is speculated that Ge diffusion is in the form of GeO or Ge-riched HfGeO. Effective suppression of Ge diffusion by NH3 nitridation has resulted in improved electrical properties of TaN∕HfO2∕Ge MOS device, including equivalent oxide thickness (EOT), leakage current, hysteresis, and interface state density. The degradation of leakage current after high temperature post metallization anneal (PMA) is found to be due to Ge diffusion.

Recently rediscovered layered black phosphorus (BP) provides rich opportunities for investigations of device physics and applications. The band gap of BP is widely tunable by its layer number and a vertical electric field, covering a wide electromagnetic spectral range from visible to mid-infrared. Despite much progress in BP optoelectronics, the fundamental photoluminescence (PL) properties of thinfilm BP in mid-infrared have rarely been investigated. Here, we report bright PL emission from thin-film BP (with thickness of 4.5 to 46 nm) from 80 to 300 K. The PL measurements indicate a band gap of 0.308 ± 0.003 eV in 46 nm thick BP at 80 K, and it increases monotonically to 0.334 ± 0.003 eV at 300 K. Such an anomalous blueshift agrees with the previous theoretical and photoconductivity spectroscopy results. However, the observed blueshift of 26 meV from 80 to 300 K is about 60% of the previously reported value. Most importantly, we show that the PL emission intensity from thin-film BP is only a few times weaker than that of an indium arsenide (InAs) multiple quantum well (MQW) structure grown by molecular beam epitaxy. Finally, we report the thickness-dependent PL spectra in thin-film BP in mid-infrared regime. Our work reveals the mid-infrared light emission properties of thin-film BP, suggesting its promising future in tunable mid-infrared light emitting and lasing applications.

We report a scalable approach to synthesize a large-area (up to 4 mm) thin black phosphorus (BP) film on a flexible substrate. We first deposited a red phosphorus (RP) thin-film on a flexible polyester substrate, followed by its conversion to BP in a highpressure multi-anvil cell at room temperature. Raman spectroscopy and transmission electron microscopy measurements confirmed the formation of a nano-crystalline BP thin-film with a thickness of around 40 nm. Optical characterization indicates a bandgap of around 0.28 eV in the converted BP, similar to the bandgap measured in exfoliated thin-films. Thin-film BP transistors exhibit a field-effect mobility of around 0.5 cm 2 /Vs, which can probably be further enhanced by the optimization of the conversion process at elevated temperatures. Our work opens the avenue for the future demonstration of largescale, high quality thin-film black phosphorus.

Highly tensile-strained Ge thin films and quantum dots have the potential to be implemented for high mobility metal-oxide-semiconductor field-effect transistor channels and long-wavelength optoelectronic devices. To obtain large tensile strain, Ge has to be epitaxially grown on a material with a larger lattice constant. We report on the growth of tensile-strained Ge on relaxed InxGa1−xAs epitaxial templates by metal-organic chemical vapor deposition. To investigate the methods to achieve high quality Ge epitaxy on III–V semiconductor surfaces, we studied Ge growth on GaAs with variable surface stoichiometry by employing different surface preparation processes. Surfaces with high Ga-to-As ratio are found to be necessary to initiate defect-free Ge epitaxy on GaAs. With proper surface preparation, tensile-strained Ge was grown on relaxed InxGa1−xAs with a range of In content. Low growth temperatures between 350 and 500 °C suppress misfit dislocation formation and strain relaxation. Planar Ge thin films with tensile strain as high as 0.5% were fabricated on relaxed In0.11Ga0.89As. For relatively high In-content (x>0.2) InxGa1−xAs templates, we observed an islanded growth morphology forming tensile-strained Ge quantum dots. Tensile strain as high as 1.37% was measured in these Ge quantum dots grown on In0.21Ga0.79As. The ability to grow these structures will enable us to further study the electronic and optoelectronic properties of tensile-strained Ge.

The spatial coherence of laser sources has limited their application to parallel imaging and projection due to coherent artifacts, such as speckle. In contrast, traditional incoherent light sources, such as thermal sources or light emitting diodes (LEDs), provide relatively low power per independent spatial mode. Here, we present a chipscale, electrically pumped semiconductor laser based on a novel design, demonstrating high power per mode with much lower spatial coherence than conventional laser sources. The laser resonator was fabricated with a chaotic, D-shaped cavity optimized to achieve highly multimode lasing. Lasing occurs simultaneously and independently in ∼1,000 modes, and hence the total emission exhibits very low spatial coherence. Speckle-free full-field imaging is demonstrated using the chaotic cavity laser as the illumination source. The power per mode of the sample illumination is several orders of magnitude higher than that of a LED or thermal light source. Such a compact, low-cost source, which combines the low spatial coherence of a LED with the high spectral radiance of a laser, could enable a wide range of high-speed, full-field imaging and projection applications.chaotic cavity | mode competition | spatial coherence S patial coherence is a defining characteristic of laser emission. High spatial coherence allows focusing electromagnetic energy to a small spot or collimation of an optical beam over a long distance. However, spatial coherence can also introduce coherent artifacts such as speckle, because any uncontrolled scattering in the imaging system can cause multipath interference. These artifacts have limited the use of lasers in full-field imaging applications ranging from traditional wide-field microscopes to laser projectors, holography, and photolithography systems. Instead, traditional low spatial coherence sources such as thermal light sources and light-emitting diodes (LEDs) are still used for illumination in most full-field imaging applications, despite having lower power per mode, poor collection efficiency, and less spectral control than lasers. These limitations are particularly pronounced in applications requiring high-speed imaging or imaging in absorbing or scattering media, prompting the use of raster-scanning-based laser imaging systems. For parallel imaging and projection applications, the ideal illumination source would combine the high power per mode of a laser with the low spatial coherence of an LED. The common approach to achieve this combination is by reducing the effective spatial coherence of a traditional laser using, e.g., a spinning diffuser (1), a colloidal solution (2), or a microelectromechanical mirror (3). However, these techniques require averaging over many speckle patterns in time, mitigating the advantage of using bright sources such as lasers or superluminescent diodes for high-speed imaging applications. Another approach to suppress speckle is by taking advantage of the low temporal coherence of broadband sources like superluminescent diodes (SLDs) ...

We have fabricated strained Ge channel ptype metal-oxide-semiconductor field-effect transistors (p-MOSFETs) on Si 0.3 Ge 0.7 virtual substrates. The poor interface between silicon dioxide (SiO 2) and the Ge channel was eliminated by capping the strained Ge layer with a relaxed, epitaxial silicon surface layer grown at 400ºC. Ge p-MOSFETs fabricated from this structure show a hole mobility enhancement of nearly 8 times that of co-processed bulk Si devices, and the Ge MOSFETs have a peak effective mobility of 1160 cm 2 /V-s. These MOSFETs demonstrate the possibility of creating a surface channel enhancement mode MOSFET with buried channellike transport characteristics.