Y. D. Sharma

nBn structure based on InAs/GaSb type-II strained layer superlattices

The authors report on a type-II InAs∕GaSb strained layer superlattice (SLS) photodetector using an nBn design that can be used to eliminate both Shockley-Read-Hall generation currents and surface recombination currents, leading to a higher operating temperature. We present such a SLS based structure with a cutoff wavelength of 5.2μm at room temperature. Processed devices exhibited a quantum efficiency around 18%, and a shot-noise-limited specific detectivity ∼109Jones at 4.5μm and 300K, which are comparable to the state of the art values reported for p-i-n photodiodes based on strained layer superlattices.

A Surface Plasmon Enhanced Infrared Photodetector Based on InAs Quantum Dots

In this paper, we report a successful realization and integration of a gold two-dimensional hole array (2DHA) structure with semiconductor InAs quantum dot (QD). We show experimentally that a properly designed 2DHA-QD photodetector can facilitate a strong plasmonic-QD interaction, leading to a 130% absolute enhancement of infrared photoresponse at the plasmonic resonance. Our study indicates two key mechanisms for the performance improvement. One is an optimized 2DHA design that permits an efficient coupling of light from the far-field to a localized plasmonic mode. The other is the close spatial matching of the QD layers to the wave function extent of the plasmonic mode. Furthermore, the processing of our 2DHA is amenable to large scale fabrication and, more importantly, does not degrade the noise current characteristics of the photodetector. We believe that this demonstration would bring the performance of QD-based infrared detectors to a level suitable for emerging surveillance and medical diagnostic applications.

Mid-IR focal plane array based on type-II InAs/GaSb strain layer superlattice detector with nBn design

A midwave infrared camera (λc=4.2μm) with a 320×256 focal plane array (FPA) based on type-II InAs∕GaSb strain layer superlattice (SLs) has been demonstrated. The detectors consist of an nBn heterostructure, wherein the SL absorber and contact layers are separated by a Al0.2Ga0.8Sb barrier layer, which is designed to have a minimum valence band offset. Unlike a PN junction, the size of the device is not defined by a mesa etch but confined by the lateral diffusion length of minority carriers. At 77K, the FPA demonstrates a temporal noise equivalent temperature difference (NETD) of 23.8mK (Tint=16.3ms and Vb=0.7V) with a peak quantum efficiency and detectivity at 3.8μm equal to 52% and 6.7×1011 Jones, respectively.

Bias dependent dual band response from InAs∕Ga(In)Sb type II strain layer superlattice detectors

We report on the multispectral properties of infrared photodetectors based on type II InAs∕Ga(In)Sb strain layer superlattices using an nBn heterostructure design. The optical and electrical properties of the midwave and long wave infrared (MWIR-LWIR) absorbing layers are characterized using spectral response and current-voltage measurements, respectively. The dual band response is achieved by changing the polarity of applied bias. The spectral response shows a significant change in the LWIR to MWIR ratio within a very small bias range (∼100mV), making it compatible with commercially available readout integrated circuits.

Low-strain InAs∕InGaAs∕GaAs quantum dots-in-a-well infrared photodetector

The authors report the design, growth, fabrication, and characterization of a low-strain quantum dots-in-a-well (DWELL) infrared photodetector. This novel DWELL design minimizes the inclusion of the lattice-mismatched indium-containing compounds while maximizing the absorption cross section by enabling larger active region volume. The improved structure uses an In0.15Ga0.85As∕GaAs double well structure with Al0.10Ga0.90As as the barrier. Each layer in the active region was optimized for device performance. Detector structures grown using molecular beam epitaxy were processed and characterized. This new design offers high responsivity of 3.9A∕W at a bias of 2.2V and a detectivity of 3×109 Jones at a bias of 2.2V for a wavelength of 8.9μm. These detectors offer significant improvement in the responsivity while retaining the long wave infrared spectral properties of the InAs∕In0.15Ga0.85As∕GaAs DWELL. These detectors if coupled with improved noise characteristics could enable higher temperature operation of ...

Performance improvement of InAs/GaSb strained layer superlattice detectors by reducing surface leakage currents with SU-8 passivation

We report on SU-8 passivation for performance improvement of type-II InAs/GaSb strained layer superlattice detectors (λcut-off∼4.6 μm). Optical and electrical behavior of SU-8 passivated and unpassivated devices was compared. The dark current density was improved by four orders of magnitude for passivated single diodes at 77 K. The zero bias responsivity and detectivity at 77 K was equal to 0.9 A/W and 3.5×1012 Jones for SU-8 passivated single pixel diodes. FPA size diodes (24×24 μm2) were also fabricated and they showed responsivity and detectivity of 1.3 A/W and 3.5×1012 Jones, respectively at 77 K.

Type II InAs∕GaSb strain layer superlattice detectors with p-on-n polarity

We report on high operating temperature midwave infrared detectors based on type II InAs∕GaSb superlattices (SLs) with a p-on-n polarity. All InAs∕GaSb SLs photodiodes reported so far have a n-on-p polarity with a thin InAs n-type top contact, that is incompatible with most present day readout integrated circuits. Current-voltage measurements reveal dark current densities of ∼5×10−7A∕cm2 (82K) and 0.18A∕cm2 (240K) at −0.1V. R0A products were equal to ∼1×105Ωcm2 (82K) and 0.24Ωcm2 (240K). Zero-biases D* were estimated to be 2×1012 and 2×109 Jones at 82 and 240K, respectively.

Mid-infrared InAs/GaSb strained layer superlattice detectors with nBn design grown on a GaAs substrate

We report on a type-II InAs/GaSb strained layer superlattice (SLS) photodetector (λ ~4.3 µm at 77 K) with nBn design grown on a GaAs substrate using interfacial misfit dislocation arrays to minimize threading dislocations in the active region. At 77 K and 0.1 V of the applied bias, the dark current density was equal to 6 × 10−4 A cm−2 and the maximum specific detectivity D* was estimated to 1.2 × 1011 Jones (at 0 V). At 293 K, the zero-bias D* was found to be ~109 Jones which is comparable to the nBn InAs/GaSb SLS detector grown on the GaSb substrate.

Reduction of surface leakage current in InAs/GaSb strained layer long wavelength superlattice detectors using SU-8 passivation

We report on SU-8 passivation for reducing surface leakage current in type-II InAs/GaSb strained layer superlattice detectors (λ100% cut-off∼12 μm). The electrical behavior of SU-8 passivated and unpassivated devices was compared for devices with variable mesa sizes. Dark current was reduced by more than one order of magnitude for the small area (50 μm×50 μm) passivated diode at 77 K. The surface resistivity, the responsivity and specific detectivity were measured for SU-8 passivated devices and are equal to 204 Ω cm, 0.58 A/W and 3.49×109 Jones, respectively (77 K).

Multi-stack InAs/InGaAs sub-monolayer quantum dots infrared photodetectors

We report on the design and performance of multi-stack InAs/InGaAs sub-monolayer (SML) quantum dots (QD) based infrared photodetectors (SML-QDIP). SML-QDIPs are grown with the number of stacks varied from 2 to 6. From detailed radiometric characterization, it is determined that the sample with 4 SML stacks has the best performance. The s-to-p (s/p) polarized spectral response ratio of this device is measured to be 21.7%, which is significantly higher than conventional Stranski-Krastanov quantum dots (∼13%) and quantum wells (∼2.8%). This result makes the SML-QDIP an attractive candidate in applications that require normal incidence.