Huong Tran

Si based GeSn photoconductors with a 1.63 A/W peak responsivity and a 2.4 μm long-wavelength cutoff

Thin-film Ge0.9Sn0.1 structures were grown by reduced-pressure chemical vapor deposition and were fabricated into photoconductors on Si substrates using a CMOS-compatible process. The temperature-dependent responsivity and specific detectivity (D*) were measured from 300 K down to 77 K. The peak responsivity of 1.63 A/W measured at 1.55 μm and 77 K indicates an enhanced responsivity due to photoconductive gain. The measured spectral response of these devices extends to 2.4 μm at 300 K, and to 2.2 μm at 77 K. From analysis of the carrier drift and photoconductive gain measurements, we have estimated the carrier lifetime of this Ge0.9Sn0.1 thin film. The longest measured effective carrier lifetime of 1.0 × 10−6 s was observed at 77 K.

Systematic study of Si-based GeSn photodiodes with 2.6 µm detector cutoff for short-wave infrared detection

Normal-incidence Ge1-xSnx photodiode detectors with Sn compositions of 7 and 10% have been demonstrated. Such detectors were based on Ge/Ge1-xSnx/Ge double heterostructures grown directly on a Si substrate via a chemical vapor deposition system. A temperature-dependence study of these detectors was conducted using both electrical and optical characterizations from 300 to 77 K. Spectral response up to 2.6 µm was achieved for a 10% Sn device at room temperature. The peak responsivity and specific detectivity (D*) were measured to be 0.3 A/W and 4 × 109 cmHz1/2W-1 at 1.55 µm, respectively. The spectral D* of a 7% Sn device at 77 K was only one order-of-magnitude lower than that of an extended-InGaAs photodiode operating in the same wavelength range, indicating the promising future of GeSn-based photodetectors.

Systematic study of Ge1−xSnx absorption coefficient and refractive index for the device applications of Si-based optoelectronics

The absorption coefficient and refractive index of Ge1−xSnx alloys (x from 0% to 10%) were characterized for the wavelength range from 1500 to 2500 nm via spectroscopic ellipsometry at room temperature. By applying physical models to fit the obtained data, two empirical formulae with extracted constants and coefficients were developed: (1) Absorption coefficient. The absorption regarding Urbach tail, indirect and direct bandgap transitions were comprehensively taken into account; (2) refractive index. The Sellmeier coefficients associated with dispersion relationship were extracted. In these formulae, the Sn composition and strain percentage were the input parameters, by inputting which the spectral absorption coefficient and spectral refractive index can be obtained. Since the absorption coefficient is key information to determine the performance of the photodetectors including operation wavelength range, responsivity, and specific detectivity, and the refractive index is very useful for the design of the anti-reflection coating for photodetectors and the layer structure for waveguides, the developed formulae could simplify the optoelectronic device design process due to their parameter-based expressions.

Si based mid-infrared GeSn photo detectors and light emitters

In this work, high performance GeSn photoconductor and light emitting diodes (LED) have been demonstrated. For the photoconductor, the high responsivity was achieved due to high photoconductive gain, which is attributed to the novel optical and electrical design. The longwave cutoff at 2.4 μm was also observed at room temperature. For LED, temperature-dependent study was conducted. The electroluminescence (EL) spectra at different temperatures were obtained and EL peak shift was observed. Moreover, the emission power at different temperatures was measured. High power emission at 2.1 μm was achieved.

High performance Ge0.89Sn0.11 photodiodes for low-cost shortwave infrared imaging

Low-cost shortwave infrared detectors have great potential for emerging civilian night-vision applications. This paper reports the characteristics of Ge0.89Sn0.11 photodiodes monolithically grown on a Si substrate that holds great promise for those applications. At room temperature, the 500 μm diameter active area device demonstrated a longwave cutoff of 2.65 μm and a responsivity of 0.32 A/W at 2 μm, which corresponds to an external quantum efficiency of 20% without any contribution from the Ge buffer layer. The measured peak specific detectivity at 300 K and 77 K is 1.7 × 109 Jones and 4.3 × 109 Jones, respectively. The specific detectivity at 77 K is only one-order-of-magnitude lower than that of the market dominating extended-InGaAs photodiode. The detailed device analysis indicated that the 700-nm thick fully relaxed high-quality GeSn absorbing layer and the modified depletion region lead to the above-mentioned device performance.Low-cost shortwave infrared detectors have great potential for emerging civilian night-vision applications. This paper reports the characteristics of Ge0.89Sn0.11 photodiodes monolithically grown on a Si substrate that holds great promise for those applications. At room temperature, the 500 μm diameter active area device demonstrated a longwave cutoff of 2.65 μm and a responsivity of 0.32 A/W at 2 μm, which corresponds to an external quantum efficiency of 20% without any contribution from the Ge buffer layer. The measured peak specific detectivity at 300 K and 77 K is 1.7 × 109 Jones and 4.3 × 109 Jones, respectively. The specific detectivity at 77 K is only one-order-of-magnitude lower than that of the market dominating extended-InGaAs photodiode. The detailed device analysis indicated that the 700-nm thick fully relaxed high-quality GeSn absorbing layer and the modified depletion region lead to the above-mentioned device performance.

GeSn-based light sources and photoconductors towards integrated photonics for the mid-infrared

GeSn-based optically pumped lasers and photoconductors have been systematically investigated. The operation wavelength of these devices covers 2–3 μm. Since GeSn technique is fully compatible with current CMOS process, the GeSn-based devices can be widely used in the area of Si integrated photonics.

Silicon-based Ge0.89Sn0.11 photodetector and light emitter towards mid-infrared applications

The GeSn alloy with Sn composition of 11% has been grown using an industry standard reduced-pressure chemical vapor deposition reactor in a single run epitaxy. Low-cost commercially available GeH4 and SnCl4 were used as Ge and Sn precursors, respectively. The material characterization showed that the threading dislocations were trapped in the Ge/GeSn interface and do not propagate to the GeSn layer, resulting in high quality material. The temperature-dependent photoluminescence study revealed that the direct bandgap GeSn alloy was achieved, as the emission intensity significantly increased at low temperature. The sample was than fabricated into photoconductive detectors and waveguide lasers. For the photodetector, the spectral response wavelength cutoff at 3.0 μm was observed. The specific detectivity of 3.5×1010 cm•Hz1/2W-1 was achieved, which is close to that of market dominating InGaAs photodetectors that are operating in the same wavelength range; For the waveguide laser, the lasing threshold pumping power density of 86.5 kW/cm2 at 10 K and the highest operating temperature of 110 K were obtained. Furthermore, the characteristic temperature was evaluated as 65 K.

Study of material and optical properties of Si x Ge 1-x-y Sn y alloys for Si-based optoelectronic device applications

A series of SiGeSn alloy samples with various Si and Sn compositions and thicknesses were grown on Ge-buffered Si substrates. The growth was conducted by using low-cost commercially available silane and germane precursors in a standard industrial reduced pressure chemical vapor deposition reactor. Si and Sn compositional- and film thickness-dependent material and optical properties have been characterized using X-ray diffraction (XRD), Raman, photoluminescence (PL), and ellipsometry spectroscopies. Moreover, thermal stability in harsh growth environment, such as in subsequent III-V growth, was studied for future multi-junction solar cell applications. In situ rapid thermal annealing at 650°C was conducted to investigate the enhanced material quality and direct bandgap emission, which were confirmed by XRD, transmission electron microscopy, Raman, and PL measurements.

CVD growth and characterization of Si x Ge 1−x−y Sn y alloys for high efficiency multi-junction solar cells

Silicon-germanium-tin films were grown by an Epsilon® RPCVD single wafer CVD deposition system to be used as an intermediate cell in high efficiency multi-junction solar cells. Material and optical characterization of the samples are performed using transmission electron microscopy, X-ray diffraction, Rutherford backscattering, Raman spectroscopy, photoluminescence, and eillpsometry techniques. Thicknesses, absorption coefficients, refractive indexes, direct and indirect bandgap transitions were measured and compared for different Sn and Si composition samples. The results show that incorporation of Si in GeSn lattice lowers the lattice size and increases the energy bandgap simultaneously.