Harshvardhan Kumar

Bio: Harshvardhan Kumar is an academic researcher from National Institute of Technology Delhi. The author has contributed to research in topics: Responsivity & Photodetector. The author has an hindex of 5, co-authored 17 publications receiving 66 citations. Previous affiliations of Harshvardhan Kumar include LNM Institute of Information Technology & National Chung Cheng University.

Metal-Semiconductor-Metal GeSn Photodetectors on Silicon for Short-Wave Infrared Applications.

Abstract: Metal-semiconductor-metal photodetectors (MSM PDs) are effective for monolithic integration with other optical components of the photonic circuits because of the planar fabrication technique. In this article, we present the design, growth, and characterization of GeSn MSM PDs that are suitable for photonic integrated circuits. The introduction of 4% Sn in the GeSn active region also reduces the direct bandgap and shows a redshift in the optical responsivity spectra, which can extend up to 1800 nm wavelength, which means it can cover the entire telecommunication bands. The spectral responsivity increases with an increase in bias voltage caused by the high electric field, which enhances the carrier generation rate and the carrier collection efficiency. Therefore, the GeSn MSM PDs can be a suitable device for a wide range of short-wave infrared (SWIR) applications.

Comprehensive Analysis and Optimal Design of Ge/GeSn/Ge p-n-p Infrared Heterojunction Phototransistors

Abstract: We present a comprehensive analysis of practical p-n-p Ge/Ge1– x Sn x /Ge heterojunction phototransistors (HPTs) for design optimization for efficient infrared detection. Our design includes a Ge1– x Sn x narrow-bandgap semiconductor as the active layer in the base layer, enabling extension of the photodetection range from near-infrared to mid-infrared to perform wide-range infrared detection. We calculate the current gain, signal-to-noise ratio (SNR), and optical responsivity and investigate their dependences on the structural parameters to optimize the proposed Ge1– x Sn x p-n-p HPTs. The results show that the SNR is strongly dependent on the operation frequency and that the introduction of Sn into the base layer can improve the SNR in the high-frequency region. In addition, the current gain strongly depends on the Sn content in the Ge1– x Sn x base layer, and a Sn content of 6%–9% maximizes the optical responsivity achievable in the infrared range. These results provide useful guidelines for designing and optimizing practical p-n-p Ge1– x Sn x HPTs for high-performance infrared photodetection.

Effect of Active Layer Scaling on the Performance of Ge 1– x Sn x Phototransistors

Abstract: The impact of scaling of the base layer on the noise performance, spectral responsivity, and frequency response of Ge/Ge1– x Sn x /Ge p-n-p heterojunction phototransistor (HPT) is presented and evaluated by simulation The proposed structure consists of Ge1– x Sn x alloy in the base layer, allowing extension of the photodetection to the mid-infrared (MIR) region, enabling photodetection over a wide range This paper also includes the effect of Sn concentration and base bias voltage on the frequency performance of the HPT In addition, various noise components and signal-to-noise ratio (SNR) are estimated as a function of base layer thickness and base resistance The simulated results show that cutoff frequency ( ${f}_{T}$ ) and maximum frequency ( ${f}_{\text {max}}$ ) are not only strongly dependent on the base layer thickness but also on the Sn composition in the base layer and applied base-bias voltage The results show that the proposed HPT provides higher ${f}_{T} >45$ GHz and SNR of >70 dB for the base layer thickness of 50 nm (with Sn = 9%) can be achieved Therefore, the GeSn p-n-p HPT is promising for future fiber-optic telecommunication and MIR applications

Effect of Defects on the Performance of Si-Based GeSn/Ge Mid-Infrared Phototransistors

Abstract: In this paper, we discuss the impact of interfaces and defects on the frequency performance of Si-based GeSn heterojunction phototransistors (HPTs) at room temperature. Furthermore, the effect of base-emitter (B-E) voltage on the spectral responsivity (SR) and detectivity (D*) has also been studied. The presented device consists of Ge1–xSnx alloy in the active layer to enhance the photodetection range. However, increasing Sn content in Ge1–xSnx causes a lattice mismatch between Ge1–xSnx and Ge virtual substrate (VS), which may increase defect density at the heterointerfaces. As a result, the diffusion length ( ${\mathrm {L_{p}}}$ ) and minority carrier lifetime ( $\tau _{{\mathrm {p}}} $ ) may decrease, thereby, degrading the performance of the device. Three major noise components such as shot noise current components at the base-emitter (B-E) and base-collector (B-C) junctions and Johnson noise have been considered for the first time to calculate the detectivity and noise-equivalent-power (NEP) of the presented device. The calculated results show that the decrease in diffusion length does not cause a significant impact on the SR, D* and internal quantum efficiency (IQE), however, it significantly degraded the cut-off frequency ( ${\mathrm {f_{T}}}$ ), maximum frequency ( ${\mathrm {f_{max}}}$ ), and sensitivity (S) of the GeSn HPT at 300 K.

Design and Modeling of High-Performance DBR-Based Resonant-Cavity-Enhanced GeSn Photodetector for Fiber-Optic Telecommunication Networks

Abstract: In this work, we present a novel distributed Bragg reflector (DBR)-based resonant-cavity-enhanced (RCE) GeSn photodetector on Si substrates to achieve high-performance photodetection in terms of responsivity and 3-dB bandwidth (BW) for the short-wave infrared (SWIR) high-speed applications. The proposed structure consists of Si/SiO2 distributed Bragg reflectors (DBRs) to enhance the performance of the device. The top and bottom DBRs create a high-quality ( ${Q}$ ) optical cavity to enable multiple pass reflection schemes to increase the responsivity and also high wavelength selectivity with a sharp response. In addition, with an increase in Sn concentration in the active ( i- GeSn) layer, the photodetection range extends to longer wavelengths due to the shrinkage of bandgap energy. The calculated result shows an enhanced 3-dB BW and responsivity as compared to the existing p-i-n PDs. Therefore, the proposed DBR-based RCE GeSn PD can be a promising device for high-speed SWIR photodetection applications.

GeSn resonant-cavity-enhanced photodetectors for efficient photodetection at the 2 µm wavelength band

Abstract: The 2 µm wavelength band has recently gained increased attention for potential applications in next-generation optical communication. However, it is still challenging to achieve effective photodetection in the 2 µm wavelength band using group-IV-based semiconductors. Here we present an investigation of GeSn resonant-cavity-enhanced photodetectors (RCEPDs) on silicon-on-insulator substrates for efficient photodetection in the 2 µm wavelength band. Narrow-bandgap GeSn alloys are used as the active layer to extend the photodetection range to cover the 2 µm wavelength band, and the optical responsivity is significantly enhanced by the resonant cavity effect as compared to a reference GeSn photodetector. Temperature-dependent experiments demonstrate that the GeSn RCEPDs can have a wider photodetection range and higher responsivity in the 2 µm wavelength band at higher temperatures because of the bandgap shrinkage. These results suggest that our GeSn RCEPDs are promising for complementary metal-oxide-semiconductor-compatible, efficient, uncooled optical receivers in the 2 µm wavelength band for a wide range of applications.

Metal-Semiconductor-Metal GeSn Photodetectors on Silicon for Short-Wave Infrared Applications.

Abstract: Metal-semiconductor-metal photodetectors (MSM PDs) are effective for monolithic integration with other optical components of the photonic circuits because of the planar fabrication technique. In this article, we present the design, growth, and characterization of GeSn MSM PDs that are suitable for photonic integrated circuits. The introduction of 4% Sn in the GeSn active region also reduces the direct bandgap and shows a redshift in the optical responsivity spectra, which can extend up to 1800 nm wavelength, which means it can cover the entire telecommunication bands. The spectral responsivity increases with an increase in bias voltage caused by the high electric field, which enhances the carrier generation rate and the carrier collection efficiency. Therefore, the GeSn MSM PDs can be a suitable device for a wide range of short-wave infrared (SWIR) applications.

Silicon-based high-responsivity GeSn short-wave infrared heterojunction phototransistors with a floating base.

Abstract: We demonstrate silicon-based $p \text{-} n \text{-} p$p-n-p floating-base GeSn heterojunction phototransistors with enhanced optical responsivity for efficient short-wave infrared (SWIR) photodetection. The narrow-bandgap GeSn active layer sandwiched between the $p \text{-} {\rm Ge}$p-Ge collector and $n \text{-} {\rm Ge}$n-Ge base effectively extends the photodetection range in the SWIR range, and the internal gain amplifies the optical response by a factor of more than three at a low driving voltage of 0.4 V compared to that of a reference GeSn $p \text{-} i \text{-} n$p-i-n photodetector (PD). We anticipate that our findings will be leveraged to realize complementary metal-oxide-semiconductor-compatible, sensitive, low driving voltage SWIR PDs in a wide range of applications.

Single-photon avalanche diodes in 0.18-µm high-voltage CMOS technology.

Abstract: We have designed and fabricated high-performance single-photon avalanche diodes (SPADs) by using 0.18-µm high-voltage CMOS technology. Without any technology customization, the SPADs have low dark-count rate, high photon-detection probability, low afterpulsing probability, and acceptable timing jitter and breakdown voltage. Our design provides a low-cost and high-performance SPAD for various applications.

Effect of Active Layer Scaling on the Performance of Ge 1– x Sn x Phototransistors

Abstract: The impact of scaling of the base layer on the noise performance, spectral responsivity, and frequency response of Ge/Ge1– x Sn x /Ge p-n-p heterojunction phototransistor (HPT) is presented and evaluated by simulation The proposed structure consists of Ge1– x Sn x alloy in the base layer, allowing extension of the photodetection to the mid-infrared (MIR) region, enabling photodetection over a wide range This paper also includes the effect of Sn concentration and base bias voltage on the frequency performance of the HPT In addition, various noise components and signal-to-noise ratio (SNR) are estimated as a function of base layer thickness and base resistance The simulated results show that cutoff frequency ( ${f}_{T}$ ) and maximum frequency ( ${f}_{\text {max}}$ ) are not only strongly dependent on the base layer thickness but also on the Sn composition in the base layer and applied base-bias voltage The results show that the proposed HPT provides higher ${f}_{T} >45$ GHz and SNR of >70 dB for the base layer thickness of 50 nm (with Sn = 9%) can be achieved Therefore, the GeSn p-n-p HPT is promising for future fiber-optic telecommunication and MIR applications