High-performance GeSn photodetector and fin field-effect transistor (FinFET) on an advanced GeSn-on-insulator platform.

We report the first demonstration of high-performance GeSn metal-semiconductor-metal (MSM) photodetector and GeSn p-type fin field-effect transistor (pFinFET) on an advanced GeSn-on-insulator (GeSnOI) platform by complementary metal-oxide-semiconductor (CMOS) compatible processes. The detection range of GeSn photodetector is extended beyond 2 µm, with responsivities of 0.39 and 0.10 A/W at 1550 nm and 2003 nm, respectively. Through the insertion of an ultrathin Al2O3 Schottky-barrier-enhancement layer, the dark current IDark of the GeSn photodetector is suppressed by more than 2 orders of magnitude. An impressive IDark of ~65 nA was achieved at an operating voltage of 1.0 V. A frequency response measurement reveals the achievement of a 3-dB bandwidth of ~1.4 GHz at an illumination wavelength of 2 µm. GeSn pFinFET with fin width (Wfin) scaled down to 15 nm was also fabricated on the GeSnOI platform, exhibiting a small subthreshold swing (S) of 93 mV/decade, a high drive current of 176 µA/µm, and good control of short channel effects (SCEs). This work paves the way for realizing compact, low-cost, and multi-functional GeSn-on-insulator opto-electronic integrated circuits.

Integration of an InSb photodetector on Si via heteroepitaxy for the mid-infrared wavelength region.

In this study, InSb p-i-n photodetectors with In0.82Al0.18Sb barrier layers were grown on a (100) 6° offcut Si substrate by heteroepitaxy via an AlSb/GaSb buffer. Based on an interfacial misfit array growth mode, the dislocations at the GaSb/Si and InSb/AlSb interfaces accommodated the lattice mismatch. The In0.82Al0.18Sb barrier layer increased the 77 K R0A of the detector. From 180 K to 300 K, the generation-recombination mechanism dominated the dark current generation in the detector and surface leakage became dominant below 120 K. The detector exhibited a 77 K responsivity of 0.475 A/W and a Johnson-noise-limited detectivity of 3.08 × 109 cmHz1/2W-1 at 5.3 µm.

Integration of InGaAs MOSFETs and GaAs/ AlGaAs lasers on Si Substrate for advanced opto-electronic integrated circuits (OEICs).

Lasers monolithically integrated with high speed MOSFETs on the silicon (Si) substrate could be a key to realize low cost, low power, and high speed opto-electronic integrated circuits (OEICs). In this paper, we report the monolithic integration of InGaAs channel transistors with electrically pumped GaAs/AlGaAs lasers on the Si substrate for future advanced OEICs. The laser and transistor layers were grown on the Si substrate by molecular beam epitaxy (MBE) using direct epitaxial growth. InGaAs n-FETs with an ION/IOFF ratio of more than 106 with very low off-state leakage and a low subthreshold swing with a minimum of 82 mV/decade were realized. Electrically pumped GaAs/AlGaAs quantum well (QW) lasers with a lasing wavelength of 795 nm at room temperature were demonstrated. The overall fabrication process has a low thermal budget of no more than 400 °C.

Floating-base germanium-tin heterojunction phototransistor for high-efficiency photodetection in short-wave infrared range.

The floating-base germanium-tin (Ge1-xSnx) heterojunction phototransistor (HPT) is designed and investigated as an efficient optical receiver in the short-wave infrared range. Simulations indicate that as the Sn content increases, the responsivity significantly increases due to a higher absorption coefficient and a larger valence band offset between Ge and Ge1-xSnx. Ge0.935Sn0.065 HPTs that incorporated high-quality Ge0.935Sn0.065 film grown by molecular beam epitaxy were fabricated, demonstrating optical response beyond wavelength of 2003 nm. At a low bias voltage of 1.0 V, optical response enhancement of ~10 times was achieved over the conventional Ge0.935Sn0.065 p-i-n photodiode. High responsivities of ~1.8 A/W at 1550 nm and ~0.043 A/W at 2003 nm were demonstrated with low dark current density of 0.147 A/cm2.

Two-micron-wavelength germanium-tin photodiodes with low dark current and gigahertz bandwidth.

We report the demonstration of a germanium-tin (Ge0.9Sn0.1) multiple-quantum-well p-i-n photodiode on silicon (Si) substrate for 2 µm-wavelength light detection. Characterization of the photodetector in both direct current (DC) and radio frequency (RF) regimes was performed. At the bias voltage of -1 V, a dark current density of 0.031 A/cm2 is realized at room-temperature, which is among the lowest reported values for Ge1-xSnx-on-Si p-i-n photodiodes. In addition, for the first time, a 3 dB bandwidth (f3dB) of around 1.2 GHz is achieved in Ge1-xSnx photodetectors operating at 2 µm. It is anticipated that further device optimization would extend the f3dB to above 10 GHz.

Monolithic integration of InGaAs n-FETs and lasers on Ge substrate.

We report the first monolithic integration of InGaAs channel field-effect transistors with InGaAs/GaAs multiple quantum wells (MQWs) lasers on a common platform, achieving a milestone in the path of enabling low power and high speed opto-electronic integrated circuits (OEICs). The III-V layers used for realizing transistors and lasers were grown epitaxially on the Ge substrate using molecular beam epitaxy (MBE). A Si-CMOS compatible process was developed to realize InGaAs n-FETs with subthreshold swing SS of 93 mV/decade, ION/IOFF ratio of more than 4 orders of magnitude with very low off-state leakage current, and a peak effective mobility of more than 2000 cm2/V·s. In addition, fabrication process uses a low overall processing temperature (≤ 400 °C) to maintain the high quality of the InGaAs/GaAs MQWs for the laser. Room temperature electrically-pumped lasers with a lasing wavelength of 1.03 µm and a linewidth of less than 1.7 nm were realized.

Suppression of dark current in germanium-tin on silicon p-i-n photodiode by a silicon surface passivation technique.

We demonstrate that a complementary metal-oxide-semiconductor (CMOS) compatible silicon (Si) surface passivation technique effectively suppress the dark current originating from the mesa sidewall of the Ge(0.95)Sn(0.05) on Si (Ge(0.95)Sn(0.05)/Si) p-i-n photodiode. Current-voltage (I-V) characteristics show that the sidewall surface passivation technique could reduce the surface leakage current density (Jsurf) of the photodiode by ~100 times. A low dark current density (Jdark) of 0.073 A/cm(2) at a bias voltage of -1 V is achieved, which is among the lowest reported values for Ge(1-x)Sn(x)/Si p-i-n photodiodes. Temperature-dependent I-V measurement is performed for the Si-passivated and non-passivated photodiodes, from which the activation energies of dark current are extracted to be 0.304 eV and 0.142 eV, respectively. In addition, the optical responsivity of the Ge(0.95)Sn(0.05)/Si p-i-n photodiodes to light signals with wavelengths ranging from 1510 nm to 1877 nm is reported.