Ge PIN Photodetector Research Articles

Low dark current lateral Ge PIN photodetector array with resonant cavity effect for short wave infrared imaging

High-performance germanium (Ge) lateral PIN photodetector (PD) arrays for short wave infrared (SWIR) imaging based on Ge-on-insulator (GOI) platform was proposed and demonstrated. The high-quality GOI platform with top-Ge layer thickness of 1.25 μm and threading dislocation density of less than 105 cm−2 was prepared by using bonding and smart-cut technology. P-type and N-type regions with centrosymmetric racetrack shapes were introduced to lower the sidewall electric field and suppress the surface leakage current of the PD. Benefiting from the high-quality of the GOI platform and the unique design of lateral active regions, a low dark current of 2 nA under −1 V with outstanding rectification ratio of 2.1 × 106 were obtained at room temperature. Through constructing a vertical resonant cavity by SiO2 passivation layer and the Si/SiO2 substrate, the responsivity at 1550 nm was enhanced to 0.46 A W−1 with a high specific detectivity of 3.09 × 1010cm·Hz1/2 ·W−1 under −1 V. Ultimately, SWIR imaging was demonstrated by a Ge lateral PIN PD line array with 1 × 8 pixels under zero bias at room temperature. The results indicate that the proposed lateral Ge PD structure holds great application potential in the field of SWIR imaging.

High efficiency coupling fibers with different types of photo detectors for the management of noise multiplication and efficient bandwidth

Abstract This work has clarified the high efficiency coupling fibers with different types of photo detectors for the management of noise multiplication and efficient bandwidth. As well as the study of the base band signal to noise base band form ratios are clarified with EDFA base band amplifier length variations. Max Q form factor with EDFA amplifier base band length variations is also demonstrated. The optimum base band electrical signal form power is simulated with EDFA base band amplifier length variations. The simulative study of Ge and InGaAs PIN photo-detectors performance evaluation are studied in the presence of the soliton transmission fiber systems. The dispersion management by the soliton technique to reach the value around zero. The max base band signal power form is clarified versus time based Ge and InGaAs PIN photo-detectors. Total base band electrical power form based Ge and InGaAs PIN photo-detectors are demonstrated. Max signal base form power amplitude band is simulated with the spectral base band frequency based Ge and InGaAs PIN photo-detectors. The max signal base form power amplitude band is studied versus time based Ge PIN photo-detectors.

PIC-integrable high-responsivity germanium waveguide photodetector in the C + L band.

We report the demonstration of a germanium waveguide p-i-n photodetector (PD) for the C + L band light detection. Tensile strain is transferred into the germanium layer using a SiN stressor on top surface of the germanium. The simulation and experimental results show that the trenches must be formed around the device, so that the strain can be transferred effectively. The device exhibits an almost flat responsivity with respect to the wavelength range from 1510 nm to 1630 nm, and high responsivity of over 1.1 A/W is achieved at 1625 nm. The frequency response measurement reveals that a high 3 dB bandwidth (f3dB) of over 50 GHz can be obtained. The realization of the photonic-integrated circuits (PIC)-integrable waveguide Ge PDs paves the way for future telecom applications in the C + L band.

Optimal Design and Noise Analysis of High-Performance DBR-Integrated Lateral Germanium (Ge) Photodetectors for SWIR Applications

This work presents the high-performance Si/SiO2 distributed Bragg reflector (DBR)-integrated lateral germanium (Ge) p-i-n photodetectors (PDs) for atmospheric gas sensing and fiber-optic telecommunication networks in the short-wave infrared (SWIR) regime. In addition, this study also proposes an optoelectronic compact small-signal noise equivalent circuit model (SSNECM) of the designed device to compute the noise performance at the detectors’ output. Various figure-of merits including current under dark and illumination, responsivity, detectivity, bandwidth, and the noise of the proposed device are estimated at the room temperature (RT) for an incident optical power of 0.5 μW. Furthermore, the impact of width and height scaling on dark current, responsivity, and bandwidth are investigated to optimize the proposed device. The validation of the proposed model is done by comparing various parameters including dark current, responsivity, and detectivity of the designed device with other Ge PDs. The estimated results show the reduced trade-off between responsivity and bandwidth of the designed device. At λ=1550 nm, the proposed device achieves a high detectivity and SNR of >2×1011Jones and 120 dB (at 3 THz), respectively, with the bias voltage of -2V. These encouraging results pave the path for the future development of low-noise and high-speed detectors.

High Performance p-i-n Photodetectors on Ge-on-Insulator Platform.

In this article, we demonstrated novel methods to improve the performance of p-i-n photodetectors (PDs) on a germanium-on-insulator (GOI). For GOI photodetectors with a mesa diameter of 10 μm, the dark current at −1 V is 2.5 nA, which is 2.6-fold lower than that of the Ge PD processed on Si substrates. This improvement in dark current is due to the careful removal of the defected Ge layer, which is formed with the initial growth of Ge on Si. The bulk leakage current density and surface leakage density of the GOI detector at −1 V are as low as 1.79 mA/cm2 and 0.34 μA/cm, respectively. GOI photodetectors with responsivity of 0.5 and 0.9 A/W at 1550 and 1310 nm wavelength are demonstrated. The optical performance of the GOI photodetector could be remarkably improved by integrating a tetraethylorthosilicate (TEOS) layer on the oxide side due to the better optical confinement and resonant cavity effect. These PDs with high performances and full compatibility with Si CMOS processes are attractive for applications in both telecommunications and monolithic optoelectronics integration on the same chip.

Plasmonics-Integrated Ge PIN-Photodetectors

Refractive index sensors can be designed for high sensitivities at small device foot-print. Using a complementary metal-oxide-semiconductor compatible process for fabrication paves the way to cheap devices enabling integrated biosensors. We present results on combining vertical Ge PIN photodetectors with metallic nanostructures such as Al nanohole arrays placed directly on top of the diode. The interaction of plasmonic resonances and photonic modes such as waveguide modes or optical modes in nanostructured photodetectors can potentially be exploited to design refractive index sensors with very high sensitivities. We discuss how the interplay of material properties and device geometry can be tailored for applications in integrated biosensing.

Design impact on the performance of Ge PIN photodetectors

This article presents the impact of epitaxial quality, contact resistance and profile of Ge PIN photodetectors (PDs) on dark current and responsivity. The PD structures were processed with either s ...

Optofluidic sensor system with Ge PIN photodetector for CMOS-compatible sensing

Vertical optofluidic biosensors based on refractive index sensing promise highest sensitivities at smallest area foot-print. Nevertheless, when it comes to large scale fabrication and application of such sensors, cheap and robust platforms for sample preparation and supply are needed - not to mention the expected ease of use in application. We present an optofluidic sensor system using a cyclic olefin copolymer microfluidic chip as carrier and feeding supply for a complementary metal-oxide-semiconductor-compatibly fabricated Ge PIN photodetector. Whereas typically only passive components of a sensor are located within the microfluidic channel, here the active device is directly exposed to the fluid, enabling top-illumination. The capability for detecting different refractive indices was verified by different fluids with subsequent recording of the optical responsivity. All components excel in their capability to be transferred to large scale fabrication and further integration of microfluidic and sensing systems. The photodetector itself is intended to serve as a platform for further sophisticated collinear sensing approaches.

Dark Current Suppression of Germanium Photodiode Using Metal-Interlayer-Semiconductor-Metal Structure with TiO2 interlayer

Germanium (Ge) photodetectors (PDs) are promising optoelectronics device for advanced Si photonics and optical interconnection due to excellent absorption property, near-infrared wavelengths, and process compatibility with Si-based complementary metal-oxide-semiconductor (CMOS). Ge metal-semiconductor-metal (MSM) PDs have many advantages over Ge PIN PDs in terms of low capacitance, high bandwidth, and process simplicity. However, Ge MSM PDs have large dark current because of a low hole barrier height induced by severe Fermi-level pinning between the metal and Ge, which results in poor sensitivity and large power consumption of PDs. In this work, the dark current of Ge MSM PD was tremendously reduced by introducing asymmetric metal-interlayer-semiconductor-metal (MISM) structure [Fig. 1]. As shown in Fig 2, a thin TiO2 layer was selected as the interlayer to reduce hole dark current by enhancing the hole Schottky barrier and the proposed structure can collect the photo current efficiently due to almost zero conduction band offset between TiO2 and Ge. Low p-type Ge wafer was used to minimize bulk defect current. To form MISM structure, TiO2 interlayer was deposited by atomic layer deposition (ALD) system at process temperature of 250 °C. To increase responsivity, finger-type PD was used with 10 um finger spacing and 10 um finger width. Metal-semiconductor (MS) contact region is defined by e-beam lithography and etched by 6:1 buffered HF, then metal-interlayer-semiconductor (MIS) contact region is defined by e-beam lithography. Cu contact was formed by e-beam evaporation and lift off process. As a result, MISM structure exhibits tremendous dark current reduction by approximately 4,000 times at a bias voltage of 1 V. The dark current reduces as the TiO2 thickness increases as shown in Fig. 3. In case of 1 nm-thick TiO2 interlayer the dark current is hardly reduced compared to symmetric MSM structure because most of holes can flow through 1 nm-thick TiO2 interlayer by tunneling. The hole dark current from the metal side diminishes as TiO2 thickness increases because hole tunneling probability decreases. The dark current with 3 nm-thick and 5 nm-thick TiO2 is reduced by 64 times and 3,970 times at 1 V, respectively, from symmetric MSM structure. As shown in Fig. 4, photo I-V measurement was carried out on asymmetric Ge MISM PD with 5 nm-thick TiO2 interlayer with collimated infrared laser (λ=1.55 um). Measured photo current value was 0.2 mA and it was saturated at 0.6 V, and the sensitivity of the PD was 24.52 at 1 V. In summary, we tremendously suppress dark current by approximately 4,000 times at 1 V using MISM structure. TiO2 interlayer of asymmetric MISM structure efficiently decrease hole dark current, and this structure can be promising structure for dark-current suppression in Ge MSM PD. Figure 1

Review—Multifunctional Technology with Monolithic Integrated THz-, Photonic- and μ-Fluidic Modules

The purpose of this work is to review requirements and challenges for the monolithic integration of different devices and modules in a baseline CMOS-process with the intention to create a multifunctional technology platform. We consider integrated modules like THz devices, i.e. complementary SiGe heterojunction bipolar transistors, silicon photonics components in particular Ge-PIN photo detectors and the wafer-level integration of micro-fluidic channels for sensor applications. However, the monolithic integration of devices and modules for novel functionalities is still a trade-off. On the one side there are requirements of the integration concept and therefore to the process steps of the dedicated module to achieve a maximum device performance. On the other side there are influences of the process steps for the module integration to the performance of the devices from the underlying baseline technology like bipolar- and CMOS-transistors or passive components. Both aspects have to be considered to enable the co-integration of new modules in order to get a technology platform for high performances and novel functionalities. We review process adaptations of the baseline technologies to enable an efficient co-integration of different modules. Moreover we discuss critical process steps with a certain thermal budget and their influence to device performances. Finally we give recommendations for process sequences to enable a wafer level co-integration of microfluidic channels into a SiGe-BiCMOS technology platform.

(Invited) Multifunctional Technology with Monolithic Integrated THz-, Photonic- and µ-Fluidic Modules

In this paper we present a multifunctional technology platform with different monolithic integrated modules like THz devices, i.e. complementary SiGe heterojunction bipolar transistors, silicon photonics components in particular Ge-PIN photo detectors and finally the wafer-level integration of µ-fluidic channels for sensor applications. Challenges during the monolithic integration of these different modules were reviewed and necessary process adaptations discussed in order to enable a co-integration.

High-performance photoreceivers based on vertical-illumination type Ge-on-Si photodetectors operating up to 43 Gb/s at λ~1550nm

We present high-sensitivity photoreceivers based on a vertical- illumination-type 100% Ge-on-Si p-i-n photodetectors (PDs), which operate up to 50 Gb/s with high responsivity. A butterfly-packaged photoreceiver using a Ge PD with 3-dB bandwidth (f(-3dB)) of 29 GHz demonstrates the sensitivities of -10.15 dBm for 40 Gb/s data rate and -9.47 dBm for 43 Gb/s data rate, at BER of 10(-12) and λ ~1550 nm. Also a photoreceiver based on a Ge PD with f(-3dB)~19 GHz shows -14.14 dBm sensitivity at 25 Gb/s operation. These results prove the high performance levels of vertical-illumination type Ge PDs ready for practical high-speed network applications.

Improvement on performance of Si-based Ge PIN photodetector with Al/TaN electrode for n-type Ge contact

Large contact resistance due to Fermi level pinning effect at the interface between metal and Ge strongly restricts the 3 dB bandwidth of Ge photodetectors. In this paper, the Ge PIN photodetectors fabricated on silicon-on-insulator substrates, respectively, with Al and Al/TaN electrodes are comparatively studied. It is found that 3 dB bandwidth of photodetector with 24 μm mesa diameter using an Al/TaN stack electrode is improved by four times more than that of the same structure Ge PIN photodetector using an Al electrode under -1 V bias at 1.55 μ. In addition, the dark current is reduced by one order of magnitude, and optical responsivity is enhanced by two times. These results suggest that a thin metallic TaN layer as an electrode can effectively passivate the Ge surface and alleviate the Fermi-level pinning effect, thus reducing the contact resistance and the recombination current at the interface. TaN can be considered as a promising electrode material for Ge device applications.

Monolithic integration and synchronous operation of germanium photodetectors and silicon variable optical attenuators

We demonstrate the monolithic integration of germanium (Ge) p-i-n photodetector (PDs) with silicon (Si) variable optical attenuator (VOAs) based on submicrometer Si rib waveguide. A PD is connected to a VOA along the waveguide via a tap coupler. The PDs exhibit low dark current of ~60 nA and large responsivity of ~0.8 A/W at the reverse bias of 1 V at room temperature. These characteristics are uniform over the chip scale. The PDs generate photocurrents precisely with respect to DC optical power attenuated by the VOAs. Two devices work synchronously for modulated optical signals as well. 3-dB cut-off frequency of the VOA is ~100 MHz, while that of the PD is ~1 GHz. The synchronous response speed is limited by the VOA response speed. This is the first demonstration, to the best of our knowledge, of monolithic integration of Ge PDs with high-carrier-injection-based optical modulation devices based on Si.

High-speed germanium photodiodes monolithically integrated on silicon with MBE

Germanium on silicon pin-photodiodes for vertical light incidence is presented. The monolithically integrated devices are grown on Si with solid source molecular beam epitaxy. The lattice mismatch between Si and Ge is adjusted with a special virtual substrate concept. This thin virtual substrate allows the integration of Ge photodiodes with Si-based circuits. For a Ge pin-photodetector with a diameter of 10 μm, a 3-dB bandwidth of 25.1 GHz is measured at an incident wavelength of 1552 nm and zero external bias. For a modest reverse bias of 2 V, the 3-dB bandwidth increases to 38.9 GHz. The whole device structure consisting of a highly p-doped Ge buried layer, an intrinsic absorption region, a highly n-doped top contact layer from Ge/Si is grown in one continuous epitaxial run. The intrinsic region of the Ge detector has a thickness of only 300 nm in order to facilitate device integration by a thin layer stack. A low growth temperature sequence was selected to obtain abrupt doping transitions between the highly doped regions surrounding the intrinsic layer. The abruptness of Ge and doping profiles was confirmed with SIMS.

An Optical Computed Tomography by Means of the Simplified Collimator in Near-infrared Region

The optical CT unit which was assembled with the laser diode working at the wavelength of 1.3 μm, and a glass optical fiber and a pin-hole with a diameter of the 100 μm yields the collimated near-infrared light through a scattering medium. Because the spatial collimator system needs no fast response time, a high sensitive Ge-PIN photodetector was employed the CT system. The optical CT image is allowed by use of near-infrared absorption characteristic. When the image construction of a grape was performed using projection data, so the comparatively good experimental results was obtained. The places of a grape seed was found without cutting. By means of the difference in characteristics of near-infrared absorption, the image of a cylindrical oil phantom in gelatin was reproduced.

High-speed interdigitated Ge PIN photodetectors

We report a high-speed PIN photodetector fabricated on Ge with planar interdigitated p/sup +/ - and n/sup +/ -fingers that were formed by ion implantation into a Ge substrate. The 3-dB bandwidth and the external quantum efficiency were measured on a photodetector having 1-μm finger width and 2-μm spacing with 50 × 50 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> active area. At a wavelength of 1.3 μm, the bandwidth was 1.8, 2.6, and 3 GHz at bias voltages of 5, 10, and 15 V, respectively. The dark current was 0.9 and 10 μA at 5 and 15 V, respectively. This photodetector exhibited external quantum efficiencies over 60% in the spectral range 1.0-1.5 μm. At a wavelength of 1.3 μm, the external quantum efficiency was 67%.