Quantum Dot Infrared Photodetectors Research Articles

Broadband Quantum-Dot Infrared Photodetector

In this letter, we report the five-period quantum-dot infrared photodetectors (QDIPs) with a bi-stacked quantum-dot (QD) structure for a wide and relatively flat detection response ranging from 4 to 11 μm with high responsivities. The bi-stacked QD structure consists of a standard InAs QD and an InGaAs-capped InAs QD layer separated by a 50-nm GaAs barrier layer. The device exhibits a wide detection window in the range of 4-11 μm with high responsivities, which suggests that similar responsivities can be obtained for the standard QD and the InGaAs-capped QD layers in the mid-wavelength (MWIR) and long-wavelength (LWIR) infrared ranges, respectively. The results are advantageous for the development of broadband QDIPs covering MWIR and LWIR ranges based on the stacked QD structures.

Increased photocurrent in quantum dot infrared photodetector by subwavelength hole array in metal thin film

Photocurrent enhancement in quantum dot (QD) infrared photodetector (QDIP) with an optical grating of subwavelength hole array in a thin metal film has been studied by calculating the transmission and diffraction of the infrared optical field through the grating and the light-matter interaction between the transmitted optical field and electrons confined in the QD. It is shown that due to the small aspect ratio of realistic QDs in QDIPs, the light diffraction due to the surface plasmon effect at the metal-semiconductor surface and the photonic subwavelength hole array structure is dominant in increasing the photocurrent.

Characteristics analysis of quantum wire infrared photodetectors under both dark and illumination conditions

This paper presents a theoretical analysis for the characteristics of quantum wire infrared photodetectors (QRIPs). Mathematical model describing this device is introduced. Maple 4 software is used to device this model. The developed model is used to investigate the behavior of the device with different values of performance parameters such as number of quantum wire layers, lateral characteristic size, and temperature. The modeling results are validated against experimental published work and full agreements are obtained. Several performance parameters are tuned to enhance the performance of these quantum photodetectors through the presented modeling. The resultant performance characteristics and comparison among both quantum well infrared photodetectors (QWIPs) and QRIPs are presented in this work. From the obtained results we notice that the total dark current in the QRIPs can be significantly lower than that in the QWIPs. Moreover, main features of the QRIPs such as the large gap between the induced photocurrent and dark current open the way for overcoming the problems of quantum dot infrared photodetectors (QDIPs).

Vertically Coupled Quantum-Dot Infrared Photodetectors

Vertically coupled InAs-GaAs quantum-dot infrared photodetectors (QDIPs) were studied in this letter. With vertically coupled quantum dots (QDs), the QDs in the same column share the same electronic states which remove the QD size variation effect in the growth direction and result in a narrow response band and higher peak quantum efficiency. The coupled states increase the capture probability and also facilitate the carrier flow among QD layers. The frequency response of vertically coupled QDIPs is much faster than that of the conventional ones.

Performance improvement of quantum dot infrared photodetectors through modeling

This paper presents a method to evaluate and improve the performance of quantum dot infrared photodetectors (QDIPs). We proposed a device model for QDIPs. The developed model accounts for the self-consistent potential distribution, features of the electron capture and transport in realistic QDIPs in dark and illumination conditions. This model taking the effect of donor charges on the spatial distribution of the electric potential in the QDIP active region. The model is used for the calculation of the dark current, photocurrent and detectivity as a function of the structural parameters such as applied voltage, doping QD density, QD layers, and temperature. It explains strong sensitivity of dark current to the density of QDs and the doping level of the active region. In order to confirm our models and their validity on the practical applications, a comparison between the results obtained by proposed models and that experimentally published are conducted and full agreement is observed. Results show the effectiveness of methodology introduced.

A Photovoltaic InAs Quantum-Dot Infrared Photodetector

A photovoltaic quantum dot infrared photodetector with InAs/GaAs/AlGaAs structures is reported. The detector is sensitive to normal incident light. At zero bias and 78K, a clear spectral response in the range of 2–7 μm has been obtained with peaks at 3.1, 4.8 and 5.7 μm. The bandgap energies of GaAs and Alo.2Gao.sAs at 78K are calculated and the energy diagram of the transitions in the Quantum-Dot Infrared Photodetector (QDIP) is given out. The photocurrent signals can be detected up to 110K, which is state-of-the-art for photovoltaic QDIP. The photovoltaic effect in our detector is a result of the enhanced band asymmetry as we design in the structure.

Optical transition and carrier relaxation in self-assembled InAs/GaAs quantum dots with InAlAs and InGaAs combination cap layer by resonant excitation

The photoluminescence (PL) spectra of self-assembled InAs/GaAs quantum dots (QDs) with InAlAs/InGaAs combination cap layer grown by molecular beam epitaxy are studied under different excitation conditions. The intrinsic optical properties of InAs QDs are investigated under resonant excitation condition. A longitudinal optical (LO) phononassisted peak can be well resolved under Eex < EgGaAs, which give evidence that the phonon-related process is dominated for carrier relaxation in InAs QDs with InAlAs/InGaAs combination cap layer when they are under resonant excitation condition. A rate equation model is established to interpret the difference of thermal activation energy (Ea). The Ea measured under Eex < EgGaAs, can exactly describe the intrinsic physical mechanism of temperature-induced quenching in InAs QDs, because it can be irrespective of the barrier materials. This result will benefit to validating the parameters of quantum dots infrared photodetector (QDIP) in sequent procedure of device fabrication.

Two-Color Qauntum-Dot Infrared Photodetectors With Periodic Cross Metal Hole Array Contact

The two-color quantum-dot infrared photodetector (QDIP) has been fabricated successfully by the use of top metal contact perforated with cross hole arrays. One transmission peak is located at 4-6 ?m; the other is located at 8-10 ?m . The periodic contact metal hole arrays play double roles, i.e., the top contact and the optical filter. Patterning with lattice constants a = 1.6 ?m and a = 2.8 ?m, the 4- to 6-?m and 8- to 11-?m wavelength ranges can be detected. The two-color QDIP detectivity can be increased up to 1.85 ×1011 cmHz1/2/W at 20 K and the background limited temperature is between 60 K-70 K. It can be applied to fabricate focal plane arrays.

Transition mechanism of InAs/GaAs quantum-dot infrared photodetectors with different InAs coverages

In this article, the authors investigate the influences of different InAs coverages on the photoluminescence excitation (PLE) spectra and spectral responses of InAs/GaAs quantum-dot infrared photodetectors (QDIPs). An increase in InAs coverage would lead to an increase in energy separation between heavy-hole state and light-hole state in the wetting layer (WL) region in the QD PLE spectra. The results suggest that most of the strain resulted from the InAs/GaAs lattice mismatch may be accumulated in the WL instead of the QD region. Also observed are the similar energy separations of energy levels responsible for the intraband absorption in the PLE spectra of the QDIPs such that similar detection wavelengths are observed for the devices.

Quantum structure based infrared detector research and development within Acreo’s centre of excellence IMAGIC

Acreo has a long tradition of working with quantum structure based infrared (IR) detectors and arrays. This includes QWIP (quantum well infrared photodetector), QDIP (quantum dot infrared photodetector), and InAs/GaInSb based photon detectors of different structure and composition. It also covers R&D on uncooled microbolometers. The integrated thermistor material of such detectors is advantageously based on quantum structures that are optimised for high temperature coefficient and low noise. Especially the SiGe material system is preferred due to the compatibility with silicon technology. The R&D work on IR detectors is a prominent part of Acreo’s centre of excellence “IMAGIC” on imaging detectors and systems for non-visible wavelengths. IMAGIC is a collaboration between Acreo, several industry partners and universities like the Royal Institute of Technology (KTH) and Linköping University.

Photodetection around 10 μm wavelength using s-p transitions in InAs/AlAs/AlGaAs self-assembled quantum dots

We propose a quantum dot infrared photodetector (QDIP) having distinct sensitivity to mutually orthogonal in-plane polarized infrared radiation, and applicable to practical infrared (IR) imaging applications. Our QDIP has either an InAs/AlAs/AlGaAs or an AlAs/InAs/AlAs/AlGaAs structure in which extra-thin AlAs layers were introduced underneath the AlGaAs buffer layer to strongly confine the carriers and also to enhance the dot density before the Stranski–Krastanov mode growth of InAs quantum dots was carried out. At 80 K, the detector has high sensitivity to in-plane orthogonally polarized infrared light, and photocurrent responsivity peaks of up to 230 mA/W associated with distinct mutually orthogonal polar lights which were observed at a wavelength of around 10.0 μm.

Wavelength-Tunable InGaAs-Capped Quantum-Dot Infrared Photodetectors

Quantum-dot infrared photodetectors (QDIPs) with InGaAs capping layers are investigated. Compared with the standard QDIP with 2.5-mono-layer (ML) InAs QDs, the detection wavelength is shifted from 6 to 7.9 ?m for an 8-nm InGaAs-capped QDIP. By decreasing the QD coverage from 2.5 to 2.0 ML, an even longer detection wavelength 10.4 ?m is observed, which is attributed to the higher energy levels of the QD excited states resulted from the smaller QDs. By further increasing the capping layer thickness to 12 nm, longer detection wavelengths with broad response 10-18 ?m is observed for the InGaAs-capped QDIP.

Review of current progress in quantum dot infrared photodetectors

AbstractQuantum dot infrared photodetectors (QDIPs) have made significant progress after their early demonstration about a decade ago. We review the progress made by QDIP technology over the last few years and compare QDIPs with quantum well infrared photodetectors (QWIPs). It is shown that the performance of QDIPs has significantly improved using novel architectures such as dots‐in‐a‐well designs, and large‐format (1 K × 1 K) focal plane arrays have been realized. However, even though there are significant reports of performance parameters better than QWIPs from single‐pixel devices, QDIP‐based focal plane arrays are still a factor of 3–5 worse in terms of noise equivalent temperature difference. We discuss the reasons for the performance gap and the key scientific and technological challenges that need to be addressed to achieve the full potential of QD‐based technology.

Quantum dot infrared photodetector enhanced by surface plasma wave excitation

Up to a thirty-fold detectivity enhancement is achieved for an InAs quantum dot infrared photodetector (QDIP) by the excitation of surface plasma waves (SPWs) using a metal photonic crystal (MPC) integrated on top of the detector absorption region. The MPC is a 100 nm-thick gold film perforated with a 3.6 microm period square array of circular holes. A bare QDIP shows a bias-tunable broadband response from approximately 6 to 10 microm associated with the quantum confined Stark (QCS) effect. On the other hand, an MPC-integrated QDIP exhibits a dominant peak at 11.3 microm with a approximately 1 microm full width at half maximum and the highly enhanced detectivity at the bias polarity optimized for long wavelength. This is very different from the photoresponse of the bare QDIP but fully consistent with the direct coupling of the QDs in the detector absorption region to the SPWs excited at the MPC/detector interface by incident photons. The SPW resonance wavelength, lambda, for the smallest coupling wavevector of the array in the MPC is close to 11.3 microm. The response also shows other SPW-coupled peaks: a significant peak at 8.1 microm (approximately lambda/radical2) and noticeable peaks at 5.8 microm (approximately lambda/2) and 5.4 microm (approximately lambda/ radical5) which correspond to higher-order coupling wavevectors. For the opposite bias, the MPC-integrated QDIP shows the highest response at 8.1 microm, providing a dramatic voltage tunability that is associated with QCS effect. SPWs propagate with TM (x, z) polarization along the MPC/detector interface. The enhanced detectivity is explained by these characteristics which increase both the effective absorption cross section with propagation and the interaction strength with TM polarization in the coupling to the QDs. Simulations show good qualitative agreement with the observed spectral behavior.

Comparative study between different quantum infrared photodetectors

This paper presents a theoretical analysis for the dark current characteristics of different quantum infrared photodetectors. These quantum photodetectors are quantum dot infrared photodetectors (QDIP), quantum wire infrared photodetectors (QRIP), and quantum well infrared photodetectors (QWIP). Mathematical models describing these devices are introduced. The developed models accounts for the self-consistent potential distribution. These models are taking the effect of donor charges on the spatial distribution of the electric potential in the active region. The developed model is used to investigate the behavior of dark current with different values of performance parameters such as applied voltage, number of quantum wire (QR) layers, QD layers, lateral characteristic size, doping quantum wire density and temperature. It explains strong sensitivity of dark current to the density of QDs/QRs and the doping level of the active region. In order to confirm our models and their validity on the practical applications, a comparison between the results obtained by proposed models and that experimentally published are conducted and full agreement is observed. Several performance parameters are tuned to enhance the performance of these quantum photodetectors through the presented modeling. The resultant performance characteristics and comparison among them are presented in this work. From the obtained results we notice that the total dark current in the QRIPs can be significantly lower than that in the QWIPs. Moreover, main features of the QRIPs such as the large gap between the induced photocurrent and dark current open the way for overcoming the problems of quantum dot infrared photodetectors.

Metal-oxide-semiconductor SiGe/Si quantum dot infrared photodetectors with delta doping in different positions

Boron was delta (δ) introduced in SiGe/Si quantum dots (the δ-QD sample) or Si spacers (the δ-spacer sample) in SiGe/Si quantum dot infrared photodetectors (QDIPs) to provide the quantum dots with a sufficient hole concentration for infrared excitation. The influence on dark currents due to the different positions of δ-doping layers is studied. The current mechanisms of the δ-QD sample and the δ-spacer sample in metal-oxide-semiconductor structures are discussed. It is found that the positions of δ-doping layers should depend on the applications of QDIPs.

Design and analysis of a new structure of InAs/GaAs QDIP for 8–12 μm infrared windows with low dark current

Based on the effective mass Schrödinger equation and eight-band k.p method, we study optical absorption in the 8–12 µm infrared window through the conduction subbands of self-assembled InAs/GaAs pyramidal shape quantum dots (QDs) using the finite difference method. Considering homogeneous and inhomogeneous broadening effects, the absorption spectra of QDs are calculated. Regarding the simulation results, we design a QD infrared photodetector (QDIP) with a double barrier resonant tunnelling (DBRT) at λ = 10 µm. We calculate the responsivity, detectivity and dark current for the device, considering the coverage factor of QDs. To enhance the performance of the presented DBRT especially at near room temperature, we propose a modified QDIP with asymmetric multiple barrier resonant tunnelling structure. With the modified structure, the dark current reduces to about half an order of magnitude compared with DBRT–QDIP, and detectivity increases to 1.4 × 109 cm Hz1/2/W at 200 K.

Outlook on quantum dot infrared photodetectors

This paper reviews the present status and gives outlook on future developments of quantum dot infrared photodetectors (QDIPs). At the beginning the paper summarizes the fundamental properties of QDIPs. Next, an emphasize is put on their potential developments. Investigations of the performance of QDIPs as compared to other types of infrared photodetectors are presented. A model is based on fundamental performance limitations enabling a direct comparison between different infrared material technologies. It is assumed that the performance is due to thermal generation in the active detector’s region. In comparative studies, the HgCdTe photodiodes, quantum well infrared photodetectors (QWIPs), type II superllatice photodiodes, Schottky barrier photoemissive detectors, doped silicon detectors, and high temperature superconductor detectors are considered.

The influence of In composition on InGaAs-capped InAs/GaAs quantum-dot infrared photodetectors

The influence of an additional InGaAs-capped layer on the performance of InAs/GaAs quantum-dot infrared photodetectors (QDIPs) is investigated. For the device with a 15% InGaAs-capped layer, a significant response at 7.9 μm is observed for the QDIP device. The results suggest that with the additional InGaAs-capped layer, the detection wavelengths of the InAs/GaAs QDIPs could be shifted to a longer-wavelength infrared range. A further increase in the In composition will not help to obtain an even longer-wavelength detection, which is attributed to the cancellation of a lower InGaAs state, and InAs-QD bandgap shrinkage resulted from the relaxed compressive strains of the InGaAs layer with a higher In composition.

InGaAs-Capped InAs–GaAs Quantum-Dot Infrared Photodetectors Operating in the Long-Wavelength Infrared Range

A ten-period InAs-GaAs quantum-dot infrared photodetector (QDIP) with 8-nm In0.15Ga0.85 As capping layer grown after quantum-dot (QD) deposition is investigated. With reduced InAs QD coverage down to 2.0 mono-layers, responses at 10.4 and 8.4 mum are observed for the device under positive and negative biases, respectively. The phenomenon is attributed to the large Stark effect resulted from the asymmetric band diagrams of the device under different voltage polarities. The demonstration of long-wavelength infrared detections with the simple structures of the InGaAs-capped QDIP is advantageous for the development of multicolor QDIP focal-plane arrays.