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abstract: Single photon detection has emerged as a method of choice for ultra sensitive measurements of picosecond optical transients. In the short wave infrared, semiconductor based single photon detectors typically exhibit relatively poor performance compared with all silicon devices operating at shorter wavelengths. Here we show a new generation of planar germanium on silicon (Ge on Si) single photon avalanche diode (SPAD) detectors for short wave infrared operation. This planar geometry has enabled a significant step change in performance, demonstrating single photon detection efficiency of 38% at 125 K at a wavelength of 1310 nm, and a fifty fold improvement in noise equivalent power compared with optimised mesa geometry SPADs. In comparison with InGaAs/InP devices, Ge on Si SPADs exhibit considerably reduced afterpulsing effects. These results, utilising the inexpensive Ge on Si platform, provide a route towards large arrays of efficient, high data rate Ge on Si SPADs for use in eye safe automotive LIDAR and future quantum technology applications.By incorporating germanium, single photon avalanche diode detectors using silicon based platforms are applied to infrared light detection. Here, a cost effective planar detector geometry is presented yielding high detection efficiency suitable for applications such as sparse photon imaging or LIDAR.
author_names: Peter Vines

Kateryna Kuzmenko

Jaroslaw Kirdoda

Derek C S Dumas

Muhammad M Mirza

Ross W Millar

Douglas J Paul

Gerald S Buller
title: High performance planar germanium on silicon single photon avalanche diode detectors
venue: Nature Communications
year: 2019

abstract: A key milestone for the next generation of high performance multifunctional microelectronic devices is the monolithic integration of high mobility materials with Si technology. The use of Ge instead of Si as a basic material in nanoelectronics would need homogeneous p and n type doping with high carrier densities. Here we use ion implantation followed by rear side flash lamp annealing (r FLA) for the fabrication of heavily doped n type Ge with high mobility. This approach, in contrast to conventional annealing procedures, leads to the full recrystallization of Ge films and high P activation. In this way single crystalline Ge thin films free of defects with maximum attained carrier concentrations of 2.20 0.11 x 1020 cm 3 and carrier mobilities above 260 cm2/(V*s) were obtained. The obtained ultra doped Ge films display a room temperature plasma frequency above 1,850 cm 1, which enables to exploit the plasmonic properties of Ge for sensing in the mid infrared spectral range.
author_names: Slawomir Prucnal

Fang Liu

Matthias Voelskow

Lasse Vines

L Rebohle

Denny Lang

Yonder Berencen

Stefan Andric

Roman Boettger

Manfred Helm

Shengqiang Zhou

Wolfgang Skorupa
title: Ultra doped n type germanium thin films for sensing in the mid infrared
venue: Scientific reports
year: 2016

abstract: Abstract We present our work on high performance germanium (Ge) quantum dot (QD) photodetectors (PDs) fabricated on Si and Ge substrates, that operate via tunneling transport through a QD containing active layer and feature high internal photoconductive gain. In the l 400 1100 nm range, the PDs fabricated on Si substrates exhibit room temperature spectral responsivity R sp up to 4 A/W and internal quantum efficiency (IQE) up to 700% At l 640 nm and 12 m W of incident power, signal to noise ratio (SNR) of 7 x 10 6 and specific detectivity D of 1.2x1011 cmHz1/2W 1 are obtained. The PDs demonstrate 3 dB bandwidths (f3dB) up to 10 MHz, corresponding to response times of 40 ns. When operated at 100 K temperature the performance improves, especially at low incident power, where at 10 nW D increases to 2 x 10 13 cmHz1/2W 1, due to IQE in excess of 22000% In order to extend the photoresponse into the near infrared (near IR) PDs were fabricated on Ge substrates, yielding room temperature R sp 1.5 A/W, IQE 134% and f3dB 10 kHz at the l 1550 nm telecommunication wavelength. Significant improvement to f3dB is expected in PDs employing thinner QD containing layers. Lowering temperature to 50 K and incident power to 10 nW yield D* 1013 cmHz1/2W 1, resulting from IQE exceeding 60000% Based on the above figures of merit, as well as their Si technology compatibility, our Ge QD PDs appear promising for high performance photodetectors working in the visible and near IR.
author_names: Stylianos Siontas

Dongfang Li

Haobei Wang

Aravind A V P S

Alexander Zaslavsky

Domenico Pacifici
title: High performance germanium quantum dot photodetectors in the visible and near infrared
venue: Materials Science in Semiconductor Processing
year: 2019

abstract: A high performance and broadband heterojunction photodetector has been successfully fabricated. The heterostructure device is based on a uniform and pinhole free perovskite film constructed on top of a single crystal germanium layer. The perovskite/germanium photodetector shows enhanced performance and a broad spectrum compared with the single material based device. The photon response properties are characterized in detail from the visible to near infrared spectrum. At an optical fibre communication wavelength of 1550 nm, the heterojunction device exhibits the highest responsivity of 1.4 A/W. The performance is promoted because of an antireflection perovskite coating, the thickness of which is optimized to 150 nm at the telecommunication band. At a visible light wavelength of 680 nm, the device shows outstanding responsivity and detectivity of 228 A/W and 1.6 x 1010 Jones, respectively. These excellent properties arise from the photoconductive gain boost in the heterostructure device. The presented heterojunction photodetector provides a competitive approach for wide spectrum photodetection from visible to optical communication areas. Based on the distinguished capacity of light detection and harvesting from the visible to near infrared spectrum, the designed germanium/perovskite heterostructure configuration is believed to provide new building blocks for novel optoelectronic devices.Perovskite germanium layers for broadband light detectionA device made from germanium and perovskite layers can detect light in the visible and near infrared ranges, showing potential for use in a wide range of applications, including in optical communications and next generation optoelectronics. This heterojunction photodetector fabricated by Chunlai Xue of the Chinese Academy of Sciences and colleagues overcomes problems in single material photodetectors, which are unable to detect a broad range of light. Recent research into various combinations of semiconducting materials for heterojunction photodetectors has led to devices with poor sensitivity to light or that require a high working voltage. Adding a layer of methylammonium lead triiodide perovskite to a layer of germanium resulted in a highly sensitive photodetector at the optical fibre communication wavelength of 1550 nm (near infrared range) and the visible light wavelength of 680 nm.
author_names: Wei Hu

Hui Cong

Wentao Huang

Yu Huang

Lijuan Chen

Anlian Pan

Chunlai Xue
title: Germanium/perovskite heterostructure for high performance and broadband photodetector from visible to infrared telecommunication band
venue: Light, science applications
year: 2019

abstract: Abstract A layered germanium phosphide (GeP3) was synthesized in a straightforward manner using a simple solid state synthetic method, and its electrochemical behavior for lithium ion batteries (LIBs) and sodium ion batteries (SIBs) was investigated. During Li insertion and extraction, the GeP3 experienced a sequential three step (topotactic transition, conversion, and alloying) and two step (dealloying and recombination) reaction. During Na insertion and extraction, GeP3 had a one step (conversion) and two step (recombination and topotactic transition) reaction. Based on the interesting phase change mechanisms during Li and Na insertion/extraction, the GeP3 based nanocomposite exhibited superior electrochemical performance, such as large reversible capacity (first reversible capacity: 1526 mAh g 1 for LIB, 984 mAh g 1 for SIB) high initial Coulombic efficiencies (86.3% for LIB, 81.3% for SIB) stable cycle life (capacity retention for LIB: 95% in 0 2 V after 30 cycles, 87% in 0.35 2 V after 100 cycles, and 93% in 0.64 2 V after 100 cycles, capacity retention for SIB: 95% in 0 2 V after 30 cycles) and rapid rate capabilities (LIB: 860 mAh g 1 in 0.35 2 V at 2C rate, SIB: 520 mAh g 1 in 0 2 V at 2C rate) Overall, the layered GeP3 based anode with its interesting Li and Na reaction mechanisms will be a promising alternative anode for high performance LIBs and SIBs.
author_names: Ki-Hun Nam

Ki-Joon Jeon

Cheol-min Park
title: Layered germanium phosphide based anodes for high performance lithium and sodium ion batteries
venue: Energy Storage Materials
year: 2019

abstract: Abstract Germanium has attracted much attention in recent decades due its intrinsic suitability for use in lithium ion batteries. It has a high capacity (1384 mA h g 1, corresponding to Li15Ge4) excellent lithium ion diffusivity (400 times faster than Si) and high electrical conductivity (104 times higher than Si) However, its range of applications is hindered by the huge volume change during the lithiation and delithiation process ~250% in a lithiated state for Li15Ge4 and ~300% for Li22Ge5) thereby resulting in electrode pulverization and its isolation from the current collector, which finally leads to the loss of capacity and poor cycling performance. Much research has been conducted to improve the electrochemical performance of germanium materials with great success in recent years. The present review focuses on the synthetic routes and novel electrode structures used for germanium anodes to obtain electrodes with excellent performance. To present these experimental results in a systematic manner, they are categorized as follows: (i) nanostructured germanium; (ii) porous anode materials; (iii) coating or doping designs; (iv) alloyed germanium materials; (v) GeO2 based anode materials; and (vi) the future outlook is considered. Finally, our personal perspectives on germanium electrode design are presented as well as suggestions for further research into novel germanium anode materials.
author_names: Zhenglin Hu

Shu Xia Zhang

Chuanjian Zhang

Guanglei Cui
title: High performance germanium based anode materials
year: 2016

abstract: Here we report the formation of high performance and high capacity lithium ion battery anodes from high density germanium nanowire arrays grown directly from the current collector. The anodes retain capacities of 900 mAh/g after 1100 cycles with excellent rate performance characteristics, even at very high discharge rates of 20 100C. We show by an ex situ high resolution transmission electron microscopy and high resolution scanning electron microscopy study that this performance can be attributed to the complete restructuring of the nanowires that occurs within the first 100 cycles to form a continuous porous network that is mechanically robust. Once formed, this restructured anode retains a remarkably stable capacity with a drop of only 0.01% per cycle thereafter. As this approach encompasses a low energy processing method where all the material is electrochemically active and binder free, the extended cycle life and rate performance characteristics demonstrated makes these anodes highly attractive for the most demanding lithium ion applications such as long range battery electric vehicles.
author_names: Tadhg Kennedy

Emma Mullane

Hugh Geaney

Michal J Osiak

Colm O'Dwyer

Kevin M Ryan
title: High performance germanium nanowire based lithium ion battery anodes extending over 1000 cycles through in situ formation of a continuous porous network.
venue: Nano letters
year: 2014

abstract: Germanium halide perovskites are an attractive alternative to lead perovskites because of their well suited optical properties for photovoltaic applications. However, the power conversion efficiencies of solar cells based on germanium perovskites remained below 0.2% so far, and also, the device stability is an issue. Herein, we show that modifying the chemical composition of the germanium perovskite, i.e. introducing bromide ions into the methylammonium germanium iodide perovskite, leads to a significant improvement of the solar cell performance along with a slight enhancement of the stability of the germanium perovskite. With substitution of 10% of the iodide with bromide, power conversion efficiencies up to 0.57% were obtained in MAGeI2.7Br0.3 based solar cells with a planar p i n architecture using PEDOT:PSS as hole and PC70BM as electron transport layer.
author_names: Indira Kopacic

Bastian Friesenbichler

Sebastian Franz Hoefler

Birgit Kunert

Harald Plank

Thomas Rath

Gregor Trimmel
title: Enhanced Performance of Germanium Halide Perovskite Solar Cells through Compositional Engineering
year: 2018

abstract: Abstract Dual porous Ge nanostructures are synthesized via two straightforward steps. Compared with conventional approaches related to porous Ge materials, different types of pores can be readily generated by adjusting the relative ratio of the precursor amounts for GeO2 and SiO2. Unlike using hard templates with different sizes for introducing secondary pores, this system makes a uniformly blended structure of porogen and active sites in the nanoscale range. When GeO2 is subjected to zincothermic reduction, it is selectively converted to pure Ge still connected to unreacted SiO2. During the reduction process, primary pores (larger than 50 nm) are formed by eliminating zinc oxide by products, while inactive SiO2 with respect to zinc metal could contribute to retaining the overall structure. Finally, the HF treatment completely leaches remaining SiO2 and formed secondary pores (micro/mesopores) to complete the dual porous Ge structure. The resulting Ge structure is tested as an anode material for lithium ion batteries. The Ge electrode exhibits an outstanding reversibility and an exceptional cycling stability corresponding to a capacity retention of 100% after 100 cycles at C/5 and of 94.4% after 300 cycles at C/2. Furthermore, multi scale pores facilitate a facile Li ion accessibility, resulting in an excellent rate capability delivering ~740 mAh g 1 at 5C.
author_names: Dohyoung Kwon

Jaegeon Ryu

Myoungsoo Shin

Gyujin Song

Dongki Hong

Kwang Soo Kim

Soo-Jin Park
title: Synthesis of dual porous structured germanium anodes with exceptional lithium ion storage performance
year: 2018

abstract: In a simple and convenient way, mesoporous germanium nanoparticles (mp Ge NPs) are prepared by a "metathesis" reaction of magnesium germanide (Mg2Ge) and zinc chloride (ZnCl2) in an autoclave at 300 degC. Investigated as anode materials for lithium ion batteries, the prepared mp Ge NPs exhibit a high capacity retention of 1048 mA h g 1 at 1 C after 1000 cycles and a high rate capacity of 727.1 mA h g 1 at 10 C in Li Ge half cells. Additionally, a 3.4 V lithium ion full cell (Ge LiCoO2) with an energy retention of 85% ~268.8 W h kg 1) over 100 cycles is achieved.
author_names: Xianyu Liu

Ning Lin

Wenlong Cai

Yingyue Zhao

Jianbin Zhou

Jianwen Liang

Yongchun Zhu

Yitai Qian
title: Mesoporous germanium nanoparticles synthesized in molten zinc chloride at low temperature as a high performance anode for lithium ion batteries.
venue: Dalton transactions
year: 2018