Resonant Cavity Enhanced Photodetectors Research Articles

InGaAs/GaAsP Superlattice Resonant Cavity-Enhanced Photodetector Fabricated on a Nominal Si(001) Substrate for Near- and Short-Wavelength Infrared Applications

InGaAs/GaAsP Superlattice Resonant Cavity-Enhanced Photodetector Fabricated on a Nominal Si(001) Substrate for Near- and Short-Wavelength Infrared Applications

GeSn resonance cavity enhanced photodetector with gold bottom reflector for the L band optical communication.

In this work, GeSn resonant cavity enhanced (RCE) p-i-n photodetectors (PDs) with 3.7% Sn content in a GeSn layer were fabricated on a silicon on insulator (SOI) substrate. The gold (Au) layer and the deposited SiO2 layer constitute the bottom reflector and top reflector of the RCE detectors, respectively. The GeSn RCE PD has three resonant peaks and its responsivity is improved about 4.5 times at 1630 nm, compared with GeSn PDs without a gold bottom mirror. The cutoff wavelength of GeSn RCE PDs is up to 1820 nm, while it is only 1730 nm for GeSn PDs without a gold reflector. The responsivity of RCE PDs at 1630 nm reaches 0.126 A/W and 3-dB bandwidth at about 36 GHz is achieved. These results indicate that the RCE structure is an effective approach for enhancing the GeSn PD performance operated at the L band.

Planar GeSn lateral p-i-n resonant-cavity-enhanced photodetectors for short-wave infrared integrated photonics.

We report normal-incidence planar GeSn resonant-cavity-enhanced photodetectors (RCE-PDs) with a lateral p-i-n homojunction configuration on a silicon-on-insulator (SOI) platform for short-wave infrared (SWIR) integrated photonics. The buried oxide of the SOI platform and the deposited SiO2 layer serve as the bottom and top reflectors, respectively, creating a vertical cavity for enhancing the optical responsivity. The planar p-i-n diode structure is favorable for complementary-metal-oxide-semiconductor-compatible, large-scale integration. With the bandgap reduction enabled by the 4.2% Sn incorporation into the GeSn active layer, the photodetection range extends to 1960 nm. The promising results demonstrate that the developed planar GeSn RCE-PDs are potential candidates for SWIR integrated photonics.

Design and calculation of type-II superlattice resonant cavity-enhanced photodetector with high quantum efficiency and low dark current

The type-II superlattice (T2SLs) infrared detector with distributed Bragg reflector (DBR) on the basis of unipolar barrier structure is investigated. The traditional binary material InAs/GaSb is used in the device, and two kinds of unipolar barrier structures, nBn and pBp, are used to reduce the generation-recombination (GR) dark current of the device. 6 periods of AlAs0.09Sb0.91/GaSb is selected as the DBR mirror. The target wavelength of DBR mirror is 3.3 μm, which is used as methane detector. The supercell is 7 ML InAs/4 ML GaSb, which has a 50% cutoff wavelength of 4 μm. The quantum efficiency (QE) of the detector with DBR mirror can reach ~ 90% at the target wavelength of 3.3 μm, and is significantly higher than that of the device without DBR mirror. The peak detectivity of pBp RCE PD is about ~1 × 1013 Jones.

A superlattice-based resonant cavity-enhanced photodetector operating in the long-wavelength infrared

The design, fabrication, and characterization of a resonant cavity-enhanced photodetector (RCE PD) operating in the long-wavelength infrared regime are demonstrated. The incorporation of the low bandgap InAs/InAs0.70Sb0.30 type-II strained-layer superlattice into the absorber layer of the detector cavity, along with the high-reflectivity (Rm > 0.9) AlAs0.08Sb0.92/GaSb distributed Bragg reflector pairs, results in resonant enhancement at 7.7–7.8 μm, which is a spectral region relevant in applications in sensing of chemical warfare agents and in medical biomarker diagnostics. These resonant wavelength peaks also display a high quality factor in the range of 76–86 and a small temperature coefficient of 0.52 nm K−1. An nBn architecture, where an Al0.71Ga0.29As0.08Sb0.92 layer acts as a barrier for majority electrons while minimizing the valence band offset with the absorber, is also incorporated into the cavity in order to improve the electrical properties of the detector. Spectral response measurements yield a peak external quantum efficiency of 14.6% and a peak responsivity of 0.91 A W−1 at 77 K and −0.8 V; meanwhile, a dark current density of 2.0 × 10−4 A cm−2 at 77 K results in a specific detectivity of 3.7 × 1010 cm Hz1/2 W−1, coming close to the theoretical background-limited D* of an ideal broadband photovoltaic detector with the superlattice composition as that of the RCE PD.

Design and Analysis of GeSn-Based Resonant-Cavity-Enhanced Photodetectors for Optical Communication Applications

We propose and analyze GeSn resonant-cavity-enhanced photodetectors (RCE-PDs) to achieve high-speed and high-responsivity photodetection for communication applications. The designed GeSn RCE-PDs comprises a Ge/GeSn/Ge p-i-n photodiode structure grown on a silicon-on-insulator (SOI) substrate and a Si/SiO2 distributed Bragg reflector (DBR). The incorporation of Sn into the active layer effectively reduced the direct bandgap energy, thereby extending the photodetection range to longer wavelengths and, thus, enhanced the optical responsivity. The buried oxide and the Si/SiO2 DBR act as the top and bottom mirrors, respectively, that considerably enhance the responsivity. We show our theoretical models to calculate the optical absorption coefficient, bandwidth, reflectivity, and responsivity, and we optimize the proposed devices to simultaneously achieve high-responsivity and high-speed operation at 1550 nm and 2000 nm. The results show that the optimized GeSn RCE-PDs can achieve a responsivity of 0.619 A/W for 6% Sn (1.02 A/W for 10% Sn) and high 3-dB bandwidth of ~58 GHz (59 GHz) at 1550 nm (2000 nm). These results show that the proposed GeSn RCE-PDs are very promising for high-performance photodetection in communication applications.

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

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.

Resonant cavity-enhanced photodetector incorporating a type-II superlattice to extend MWIR sensitivity.

Mid-infrared resonant cavity-enhanced photodetectors (RCE PD) present a promising technology for targeted gas detection. We demonstrate an RCE PD incorporating an InAs/InAsSb superlattice as the detecting element, extending the resonant wavelength beyond 4 µm. AlAsSb/GaSb mirrors and a unipolar barrier active region paralleling an nBn structure are also used, and performance is compared to a conventional broadband nBn detector incorporating the same superlattice. The RCE PD exhibited a Q-factor of ∼90 and an extremely stable resonance wavelength. Peak responsivity was 3.0 A W-1 at 240 K, equalling 84% quantum efficiency, a 5.5 times increase over the reference nBn at the same wavelength. Dark current density was 3.3×10-2 A cm-2 at 240 K, falling to 2.7×10-4 A cm-2 at 180 K. The broadband BLIP limit is approached at 180 K with specific detectivity of 2.1×1011 cm Hz1/2 W-1, which presents the potential of achieving BLIP-limited operation in the thermoelectric cooling regime.

Design and study of a long-wavelength monolithic high-contrast grating resonant-cavity-enhanced photodetector

Novel construction of a resonant-cavity-enhanced photodetector (RCE-PD) with monolithic high-contrast grating (HCG) is proposed to overcome the difficulty of fabricating a high reflective mirror of RCE-PD at 1 550 nm. In this structure, HCG serves as the top mirror of the RCE-PD, whereas InGaAs serves as a sacrificial layer to achieve monolithic integration. During the bandwidth optimization, the ratio of the thickness of the total intrinsic region and the absorption layer is introduced to realize the simultaneous optimization of the thickness of spacing layers and absorption layer. After structural optimization, the quantum efficiency of the device with diameter of 20 μm is 82% at 1 550 nm, and the 3-dB bandwidth is 34 GHz at a bias of 3 V.

GeSn resonant-cavity-enhanced photodetectors on silicon-on-insulator platforms

We report GeSn p-i-n resonant-cavity-enhanced photodetectors (RCEPDs) grown on silicon-on-insulator substrates. A vertical cavity, composed of a buried oxide as the bottom reflector and a deposited SiO2 layer on the top surface as the top reflector, is created for the GeSn p-i-n structure to enhance the light-matter interaction. The responsivity experiments demonstrate that the photodetection range is extended to 1820nm, completely covering all the telecommunication bands, because of the introduction of 2.5% Sn in the photon-absorbing layer. In addition, the responsivity is significantly enhanced by the resonant cavity effects, and a responsivity of 0.376A/W in the telecommunication C-band is achieved that is significantly higher than that of conventional GeSn-based PDs. These results demonstrate the feasibility of CMOS-compatible, high-responsivity GeSn-based PDs for shortwave infrared applications.

A full-duplex working integrated optoelectronic device for optical interconnect

In this paper, a full-duplex working integrated optoelectronic device is proposed. It is constructed by integrating a vertical cavity surface emitting laser (VCSEL) unit above a resonant cavity enhanced photodetector (RCE-PD) unit. Analysis shows that, the VCSEL unit has a threshold current of 1 mA and a slop efficiency of 0.66 W/A at 849.7 nm, the RCE-PD unit obtains its maximal absorption quantum efficiency of 90.24% at 811 nm with a FWHM of 4 nm. Moreover, the two units of the proposed integrated device can work independently from each other. So that the proposed integrated optoelectronic device can work full-duplex. It can be applied for single fiber bidirectional optical interconnects system.

Temporal Response of Dilute Nitride Multi-Quantum-Well Vertical Cavity Enhanced Photodetector

The temporal response characteristics of a GaInNAs-based vertical resonant cavity enhanced photodetector device are presented for operation at λ ≈ 1.3 μm. The absorption layers of the device are composed of nine 7-nm-thick Ga0.65In0.35N0.02As0.98 quantum wells and are sandwiched between top and bottom AlGaAs/GaAs distributed Bragg reflectors (DBRs). The temperature dependence of the transient photoconductivity (TPC) under different light intensities and bias voltages is reported. Photoluminescence measurements were also performed on structures with and without the top DBR to determine their optical response under continuous illumination. The response time was measured using excitation from a 1047-nm pulsed neodymium-doped yttrium lithium fluoride laser with pulse width of 500 ps and repetition rate of 1 kHz. The rise time of the TPC was 2.27 ns at T = 50 K, decreasing to 1.79 ns at T = 300 K. The TPC decay time was 25.44 ns at T = 50 K, decreasing to 16.58 ns at T = 300 K. With detectivity of $$ 2.28 \times 10^{10} \,{\hbox{cm}}\sqrt {\hbox{Hz}} / {\hbox{W}} $$ and noise-equivalent power of $$ 2.45 \times 10^{ - 11} \,{\hbox{W/}}\sqrt {\hbox{Hz}} $$ , the proposed device is faster and more sensitive with better signal-to-noise ratio compared with other GaInNAs-based resonant cavity enhanced photodetectors (RCEPDs) for operation at 1.3 μm.

Characterization of temperature dependent operation of a GaInNAs-based RCEPD designed for 1.3 μm

We report the characteristics of the temperature dependent operation of a GaInNAs-based resonant-cavity-enhanced photodetector (RCEPD), designed to be operated at the dispersion minimum optical communication window of 1.3 μm. A Transfer-Matrix Method (TMM) was used to design the structure of the device. The absorption layer of the photodetector is comprised of nine 7 nm-thick Ga0.733In0.267N0.025As0.975(Sb)/GaN0.035As0.965 quantum wells, and 15 and 10 pairs of GaAs/AlAs distributed Bragg reflectors (DBRs) grown as the bottom and top mirrors, to form the cavity of the device. All electrical and optical measurements were carried out over a temperature range from 10 to 40 °C in order to investigate the characteristic of the device. The quantum efficiency is determined to be in the range of 16% (at 10 °C) and 31% (at 40 °C). An excellent wavelength selectivity is observed which changed from 3.7 nm (at 10 °C) to 5.4 nm (at 40 °C). The dark current of the device is measured as 11 nA at 10 °C and 19 nA at 40 °C without bias. The photocurrent at −0.5 V is measured to be 1.5 mA at 25 °C. The high dark current of the device is attributed to weak confinement of the electrons in GaInNAs QW surrounded by the strain-compensator GaNAs barrier layers. The temperature dependent cavity wavelength was analytically calculated and compared with that of experimental results. The temperature dependent linear shifts of the resonance wavelength (dλ/dT) is calculated as 0.077 nm/°C, which is in good agreement with the experimental result, 0.080 nm/°C. Our results reveal that the characteristics of a RCEPD, such as quantum efficiency, FWHM etc., are quite sensitive to temperature changes due to the temperature dependence of the refractive index of the DBRs.

Hybrid III-V/SOI resonant cavity enhanced photodetector.

A hybrid III-V/SOI resonant-cavity-enhanced photodetector (RCE-PD) structure comprising a high-contrast grating (HCG) reflector, a hybrid grating (HG) reflector, and an air cavity between them, has been proposed and investigated. In the proposed structure, a light absorbing material is integrated as part of the HG reflector, enabling a very compact vertical cavity. Numerical investigations show that a quantum efficiency close to 100 % and a detection linewidth of about 1 nm can be achieved, which are desirable for wavelength division multiplexing applications. Based on these results, a hybrid RCE-PD sample has been fabricated by heterogeneously integrating an InP-based material onto a silicon-on-insulator wafer and has been characterized, which shows a clear enhancement in photo-current at the designed wavelength. This indicates that the HG reflector provides a field enhancement sufficient for RCE-PD operation. In addition, a capability of feasibly selecting the detection wavelength during fabrication as well as a possibility of realizing silicon-integrated bidirectional transceivers are discussed.

RCEPD With Enhanced Light Absorption by Crown-Shaped Quantum Well

A high-performance resonant cavity enhanced photodetector (RCEPD) is developed by introducing an InGaAs/GaAs crown-shaped quantum well (CSQW) structure. In calculation, the absorption coefficient of the proposed CSQW structure is significantly enhanced by 47.8% compared with that of the conventional QW without increasing the electric field due to the large overlap of electron/hole-wave functions. To verify the feasibility of our proposed QW structure, we fabricate RCEPDs with a designed CSQW and the conventional QW structure. The fabricated CSQW-RCEPD exhibits a maximum quantum efficiency of 45.4%, an improvement of 36.2% in comparison with the conventional RCEPD. Moreover, the spectral bandwidth is 4.7 nm in the CSQW-RCEPD, which is in good agreement with the calculated result. The RCEPD with enhanced light absorption using a CSQW structure is highly promising for optical interconnect and sensing applications.

Dilute nitride resonant cavity enhanced photodetector with internal gain for the λ ∼ 1.3 μm optical communications window

We report on a novel dilute nitride-based resonant cavity enhanced photodetector (RCEPD) operating at 1.286μm. The RCEPD was fabricated using 21 pairs top and 24 pairs bottom GaAs/AlGaAs distributed Bragg reflectors for mirrors and 7nm thick nine GaAs/Ga0.65In0.35N0.02 As0.98 quantum wells as the absorption region.For a 15μm diameter window, the photocurrent at 1.286μm is 27μA and 42μA, at V=0 and −1V, respectively, whereas the dark current is as low as 1.7nA at −1V. At the operating wavelength, an excellent wavelength selectivity with a full width at half maximum (FWHM) of 5nm, and a high quantum efficiency of 43% are demonstrated. The device exhibits significant internal gain at very small reverse bias voltages of V⩾−2V with an overall quantum efficiency of 67%. These are the best ever recorded values for a dilute nitride RCEPD.

Reflective displacement sensors with monolithically integrated VCSELs and RCEPDs

Micro-scale, reflective-type optical displacement sensors have been developed by monolithic integration of vertical cavity surface-emitting lasers (VCSELs) and resonant cavity-enhanced photodetectors (RCEPDs). This compact sensor (700 × 700 μm) consists of an oxide-confined VCSEL that is surrounded by an RCEPD and can measure the linear distance with a measurement range of ~10 mm, which is comparable to that of conventional displacement sensors. Fabrication details and sensor performances are discussed.

Recent Approaches for Broadening the Spectral Bandwidth in Resonant Cavity Optoelectronic Devices

Resonant cavity optoelectronic devices, such as vertical cavity surface emitting lasers (VCSELs), resonant cavity enhanced photodetectors (RCEPDs), and electroabsorption modulators (EAMs), show improved performance over their predecessors by placing the active device structure inside a resonant cavity. The effect of the optical cavity, which allows wavelength selectivity and enhancement of the optical field due to resonance, allows the devices to be made thinner and therefore faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. However, the narrow spectral bandwidth significantly reduces operating tolerances, which leads to severe problems in applications such as optical communication, imaging, and biosensing. Recently, in order to overcome such drawbacks and/or to accomplish multiple functionalities, several approaches for broadening the spectral bandwidth in resonant cavity optoelectronic devices have been extensively studied. This paper reviews the recent progress in techniques for wide spectral bandwidth that include a coupled microcavity, asymmetric tandem quantum wells, and high index contrast distributed Bragg-reflectors. This review will describe design guidelines for specific devices together with experimental considerations in practical applications.

Selecting detection wavelength of resonant cavity-enhanced photodetectors by guided-mode resonance reflectors

We propose and demonstrate a novel device structure of resonant cavity-enhanced photodetector (RCE-PD). The new RCE-PD structure consists of a bottom distributed Bragg reflector (DBR), a cavity with InGaAs multiple quantum wells (MQWs) for light absorption and a top mirror of sub-wavelength grating. By changing the fill factor of the 2-D grating, the effective cavity length of RCE-PDs can be varied so the resonant wavelength can be selected post growth. Accordingly, we can fabricate an array of PDs on a single chip, on which every PD aims for a specific wavelength.

Resonant cavity enhanced (RCE) photodetectors with flat-top and steep-edge spectral response

Flat-top and steep-edge spectral response of photodetectors is important for dense wavelength-division-multiplexed system. Realization of the flat-top and steep-edge response is very challenging. In the last two decades many methods have been proposed, but the spectral response linewidth is not acceptable to wavelength-division-multiplexes system. In this paper a novel RCE photodetector with flat-top and steep-edge spectral response is presented. Using the step shaped structure, designing multiple-step-type p-type In 0.67Ga 0.33As 0.7P 0.3 contact layer and adjusting the thickness of the absorption layer, a design with good flat-top performance is demonstrated such that the quantum efficiency is 51.161% in the flat-top passband, 0.5 and 3 dB bandwidths are 0.26 and 0.4 nm, respectively.