Efficient Carbon Nanotube Photodiodes A single photon absorbed in a single-walled carbon nanotube device can generate multiple unbound particles carrying an electric charge. Gabor et al. (p. 1367) report that in such a device at low temperatures, excitation with light of increasing energy leads to well-defined stepwise increases in current. Interestingly, because of the unique band structure of carbon nanotubes, this behavior is analogous to particle-antiparticle creation commonly observed in high-energy particle physics. These observations point to the promise of investigations in other nanoscale carbon systems, such as graphene, and could lead to numerous applications, including highly sensitive photon detection and ultra-efficient photovoltaics. The decay of photoexcited electrons in a carbon nanotube device creates multiple pairs of charge carriers. We observed highly efficient generation of electron-hole pairs due to impact excitation in single-walled carbon nanotube p-n junction photodiodes. Optical excitation into the second electronic subband E22 leads to striking photocurrent steps in the device I-VSD characteristics that occur at voltage intervals of the band-gap energy EGAP/e. Spatially and spectrally resolved photocurrent combined with temperature-dependent studies suggest that these steps result from efficient generation of multiple electron-hole pairs from a single hot E22 carrier. This process is both of fundamental interest and relevant for applications in future ultra-efficient photovoltaic devices.

https://www.lassp.cornell.edu/lassp_data/mceuen/homepage/Publications/Gabor_Science_2009_supmat.pdf

Supporting Online Material for Extremely Efficient Multiple Electron-Hole Pair Generation in Carbon Nanotube Photodiodes

Two-dimensional layered materials (2DLMs) have attracted a tremendous amount of attention as photodetectors due to their fascinating features, including high potentials in new-generation electronic devices, wide coverage of bandgaps, ability to construct van der Waals heterostructures, extraordinary light–mass interaction, strong mechanical flexibility, and the capability of enabling synthesis of 2D nonlayered materials. Until now, most attention has been focused on the well-known graphene and transition metal dichalcogenides (TMDs). However, a growing number of functional materials (more than 5619) with novel optoelectronic and electronic properties are being re-discovered, thereby widening the horizon of 2D libraries. In addition to showing common features of 2DLMs, these new 2D members may bring new opportunities to their well-known analogues, like wider bandgap coverage, direct bandgaps independence with thickness, higher mechanical flexibility, and new photoresponse phenomena. The impressive results communicated so far testify that they have shown high potentials with photodetections covering THz, IR, visible, and UV ranges with comparable or even higher performances than well-known TMDs. Here, we give a comprehensive review on the state-of-the-art photodetections of two-dimensional materials beyond graphene and TMDs. The review is organized as follows: fundamentals of photoresponse first are discussed, followed by detailed photodetections of new 2D members including both layered and non-layered ones. After that, photodiodes and hybrid structures based on these new 2D materials are summarized. Then, the integration of these 2D materials with flexible substrates is reviewed. Finally, we conclude with the current research status of this area and offer our perspectives on future developments. We hope that, through reading this manuscript, readers will quickly have a comprehensive view on this research area.

/pdf/2d-library-beyond-graphene-and-transition-metal-2hfbrm4oqj.pdf

2D library beyond graphene and transition metal dichalcogenides: a focus on photodetection

A new semiconductor alloy material, GaAs1-xBix has been created by Metal Organic Vapor Phase Epitaxial (MOVPE) growth. A low growth temperature, such as 365°C, is required to obtain the alloy. X-ray diffraction measurements of alloy layers reveal that the diffraction patterns are satisfactory. The maximum GaBi content in the GaAsBi alloy estimated from the lattice constant is around 2%, which is consistent with that estimated from secondary ion mass spectroscopy (SIMS) measurements. In a photoluminescence (PL) measurement, a single peak spectrum is observed from 10 to 300 K. The temperature variation of the PL peak energy is as small as 0.1 meV/K.

New Semiconductor Alloy GaAs_ Bi_x Grown by Metal Organic Vapor Phase Epitaxy

Plasmonic photodetectors are attracting the attention of the photonics community. Plasmonics is attractive because metallic structures have the ability to confine light by coupling an electromagnetic wave to charged carrier oscillations at the surface of the metal. The wavelength of such oscillations can be much smaller than the corresponding light wavelength in vacuum. This enables the light-matter interaction on a deep subwavelength scale, which in turn allows for more compact and potentially higher speed devices. In this review, we discuss different types of photodetectors and ways in which plasmonics can be applied to them. We elucidate several plasmonic photodetector concepts/schemes and discuss the main physical principles behind their operation. Finally, we reflect on the characteristics of an “ideal” photodetector and propose a device that might be the perfect plasmonic detector.

Plasmonic Photodetectors

Dilute bismide in which a small amount of bismuth is incorporated to host III-Vs is the least studied III-V compound semiconductor and has received steadily increasing attention since 2000. In this paper, we review theoretical predictions of physical properties of bismide alloys, epitaxial growth of bismide thin films and nanostructures, surface, structural, electric, transport and optic properties of various binaries and bismide alloys, and device applications.

Novel Dilute Bismide, Epitaxy, Physical Properties and Device Application

The peculiar properties of the gapless surface states with a Dirac cone shaped energy dispersion in topological insulators (TIs) enable promising applications in photodetection with an ultra-broad band and polarization sensitivity. Since many TIs can be easily grown on silicon (Si) substrates, TIs on Si could make an alternative route for photon detection of Si photonics. We present good device performances of a Si-based single-crystal bismuth telluride (Bi2Te3) photoconductive detector. Room temperature photo responses to 1064 nm and 1550 nm light illumination were demonstrated. Linear dependences of the photocurrent on both the incident light power and the bias voltage were observed. The main device parameters including responsivity and quantum efficiency were extracted.

http://publications.lib.chalmers.se/records/fulltext/249333/local_249333.pdf

Bi2Te3 photoconductive detectors on Si

This work reports on the demonstration of a short-wave infrared detector nearly lattice matched to InP substrate using quaternary InGaAsBi as the absorption layer. The bismuth content of about 3.2% has red-shifted the 50% cut-off wavelength from about 1.6 μm to 2.1 μm at room temperature, indicating a bandgap reduction of about 180 meV due to bismuth incorporation. The detector shows an encouraging dark current density of 2.4 × 10−4 A/cm2 at bias voltage of −10 mV at 300 K. This work shows the promising potential of InP-based lattice-matched InGaAsBi detectors for short-wave infrared detection.

Nearly lattice-matched short-wave infrared InGaAsBi detectors on InP

We report on InP-based metamorphic In0.83Ga0.17As photodetectors with dramatically suppressed dark currents by inserting a strain-compensated In0.66Ga0.34As/InAs superlattice electron barrier in the In0.83Ga0.17As absorption layer. Compared with a reference detector without the barrier, the device showed that the dark current is reduced by about half at room temperature and is more than two orders of magnitude at 77 K at low bias, while the responsivity remained unchanged. The generation recombination and tunneling currents are significantly suppressed, and the dark current remains diffusion-current-limited above 175 K. The dark current density at −10 mV is reduced to 3.95 nA/cm2 at 175 K.

https://iopscience.iop.org/article/10.7567/APEX.8.022202/pdf

Dark current suppression in metamorphic In0.83Ga0.17As photodetectors with In0.66Ga0.34As/InAs superlattice electron barrier

We present tailoring of the performances of thin multiplication layer InAlAs/InGaAs avalanche photodetectors (APDs) with operating voltages lower than 20 V. Their operating voltages, gain-voltage slopes and dark currents were successfully tailored by changing the electric field distributions in avalanche region. The thin multiplication layer APDs show small activation energies of the dark current ranging from 0.12 to 0.19 eV at temperatures above 220 K, suggesting a band-trap-band tunneling dominant dark current mechanism over this temperature range. The dark currents show very weak temperature dependences at temperatures lower than 175 K, which mainly originate from the band-to-band tunneling and the surface leakage currents. The spectral responsivity of those APDs show anomalous negative temperature coefficients at gain factors larger than 1, which is attributed to the enhanced phonon scattering effect of carriers in the avalanche region at higher temperatures. Good gain factor uniformity at a given bias is observed for those APDs, and the charge layer is found to help improve the gain uniformity.

Tailoring the performances of low operating voltage InAlAs/InGaAs avalanche photodetectors

Effects of mesa etching and geometry on InGaAs/InAlAs avalanche photodiodes (APDs) were investigated by using both wet and inductively coupled plasma (ICP) etching with different mesa shapes as well as etchants. It was found that the mesa geometry had no evident impact on APDs’ characteristics regardless of the etching techniques applied. Besides, ICP-etched APDs showed faster punch-through, suppressed premature surface breakdown and lower dark current behaviors compared to the wet-etched devices. Substantially suppressed surface leakage was also observed for ICP-etched devices, showing 1 and 3 orders of magnitude better at room temperature and 77 K respectively, and over 1 order of magnitude higher surface resistivity up to 4×107 Ω cm, in comparison to the wet-etched APDs. Introduction of extra hydrogen and Ar plasma in ICP etching led to detrimental effects to APDs’ performance by enhancing the tunneling or recombination at surfaces. Those experimental results were clearly interpreted based on the surface state theories.

Yingjie Ma

Papers

Bi2Te3 photoconductive detectors on Si

Nearly lattice-matched short-wave infrared InGaAsBi detectors on InP

Dark current suppression in metamorphic In0.83Ga0.17As photodetectors with In0.66Ga0.34As/InAs superlattice electron barrier

Tailoring the performances of low operating voltage InAlAs/InGaAs avalanche photodetectors

Impact of etching on the surface leakage generation in mesa-type InGaAs/InAlAs avalanche photodetectors.