We report on InGaAsSb infrared photodetector and light emitting diode for short wavelength infrared detection and emission. The InGaAsSb samples were grown by molecular beam epitaxy (MBE) system on a GaSb substrate. In order to investigate the structural properties of InGaAsSb layer, we took a high resolution XRD and low voltage SEM. The InGaAsSb devices were processed in 400×400 μm2 using inductively coupled plasma etching. We have measured the spectral response of InGaAsSb based photodetector using various temperature and bias. The cut-off wavelength of photodetector was 3.0 μm at room temperature. We also report an electroluminescence of InGaAsSb LED. Keywords: Short wavelength infrared, photodetector, light emitting diode, InGaAsSb, GaSb.
We report on InAs SML QD infrared photodetector performance for long wavelength infrared detection. The device
structure consists of InAs SML QDs embedded in InxGa1-xAs quantum well (QW) surrounded by GaAs and AlxGa1-
xAs barrier. In order to investigate the structural properties of SML QDs, we took cross-sectional STEM images. We
have measured the polarization dependent spectral response of SML-QD based photodetector using various angular inplane
and out-plane polarizations. We also report a systematic approach for controlling the intersubband transition
energy level in SML QD infrared photodetectors, in order to control the peak wavelength of the device.
We have investigated optical properties and figures of merit of sub-monolayer quantum dots (SML-QD) infrared
photodetector and compared them with conventional Stranski-Krastanov quantum dots (SK-QD) with a similar design.
The purpose of this study is to examine the effects of varying the number of stacks(2,3,4,5 and 6) in SML-QD detector
on its device performance The peak of photoluminescence (PL) spectra of SK-QD and SML-QDs are observed at
1.07eV and 1.24~1.35eV at room temperature, respectively. The PL peak of 2 and 3 stacks SML QD are very close to
the GaAs band edge peak (1.42eV) and the full width at half maximum (FWHM) of all the SML-QD are much narrower
than SK-QD. Normal incidence photoresponse peak of 4 stacks SML QDIP are obtained at 7.5μm with responsivity of
0.5 A/W and detectivity of 1.2×1011 cm.Hz1/2/W (77K, 0.4V, f/2 optics), which is much narrower than spectral response
of SK QDIP possibly due to bound-to-bound transition.
Next generation infrared photodetector technology will require focal plane array (FPA) systems that have multi-spectral
imaging capabilities. One proposed approach to realizing these multicolor devices is to use plasmonic resonators.
However, device development and characterization are commonly addressed with large front side illuminated single
pixel detectors on a supporting epitaxial substrate. The focal plane arrays on the other hand are backside illuminated.
Moreover, in a front side illuminated device, there is significant substrate scattering of the incident light. Here, we
propose a method for the accurate measurement of device performance by using a hybridized chip design (hybrid chip)
that is similar to the fabrication of an FPA system, with the substrate completely removed through a combination of
mechanical polishing and subsequent wet etching techniques. The hybrid chip was also designed to precisely
characterize the effects of varying mesa size by incorporating square mesa structures that range from 25 to 200 μm in
width. This approach offers an advantage over conventional device characterization because it incorporates mesas that
are on the same scale as those normally used in FPA systems, which should therefore provide a fast transition of new
photodetector technology into camera based systems. The photodetector technology chosen for this work is a multi-stack
quantum dots-in-a-well (DWELL) structure designed to absorb electromagnetic radiation in the mid-infrared spectral
We report on the performance of multi-stack quantum dots in a well (DWELL) detectors. Present-day QD detectors are
limited by low responsivity and quantum efficiency (QE). This can be attributed to the low absorption efficiency of
these structures due to the small number of QD stacks in the detector. In this paper we examine the effect of the number
of stacks on the performance of the detector. In particular, we investigate the InAs/GaAs/AlGaAs D-DWELL (Dots-in-double-well) design, which has a lower strain per DWELL stack than the InAs/InGaAs/GaAs DWELLs thereby enabling
the growth of many more stacks in the detector. The purpose of the study detailed in this paper is to examine the effects
of varying the number of stacks in the InAs/InGaAs/GaAs/AlGaAs D-DWELL detector, on its device performance. The
numbers of stacks grown using solid source molecular beam epitaxy (MBE), were 15, 30, 40, 50, and 60. Once
fabricated as single pixel devices, we carried-out a series of device measurements such as spectral response, dark current,
total current, responsivity along with computing the photoconductive gain and the activation energies. The goal of these
experiments is to not only study the single pixel detector performance with varying number of stacks in a D-DWELL
structure, but to also understand the effect of the transport mechanism in these devices.
The development of type-II InAs/GaSb superlattice (SL) detectors with nBn and pin designs for the long wave
infrared (LWIR) spectral region are discussed. First, SL growth optimization for LWIR region is explained,
then the structures based on LWIR nBn and pin are presented. Comparison of optical characterization for the
identical SL structures based on the nBn and pin designs is reported. Dark current density of 0.001 A/cm2 at
100 mV for nBn as compared to 0.2 A/cm2 for pin devices shows a reduction of dark current density using the
nBn design. At 77 K, the peak responsivity and detectivity are measured to be 5.86 A/W and 3.08 × 1010 Jones
for the nBn and 1.49 A/W and 4.2 × 109 Jones for the pin based design, respectively.
In our research group, we develop novel dots-in-a-well (DWELL) photodetectors that are a hybrid of the quantum dot
infrared photodetector (QDIP). The DWELL detector consists of an active region composed of InAs quantum dots
embedded in InGaAs quantum wells. By adjusting the InGaAs well thickness, our structure allows for the manipulation
of the operating wavelength and the nature of the transitions (bound-to-bound, bound-to-quasibound and bound-to-continuum)
of the detector. Based on these principles, DWELL samples were grown using molecular beam epitaxy and
fabricated into 320 x 256 focal plane arrays (FPAs) with Indium bumps using standard lithography at the University of
New Mexico. The FPA evaluated was hybridized to an Indigo 9705 readout integrated circuit (ROIC) in collaboration
with QmagiQ LLC and tested with a CamIRaTM system manufactured by SE-IR Corp. From this evaluation, we report
the first two-color, co-located quantum dot based imaging system that can be used to take multicolor images using a
single FPA. We demonstrated that we can operate the device at an intermediate bias (Vb=-1.25 V) and obtain two color
response from the FPA at 77K. Using filter lenses, both MWIR and LWIR responses were obtained from the array at the
same bias voltage. The MWIR and LWIR responses are thought to be from bound states in the dot to higher and lower
lying states in the quantum well respectively. Temporal NEDT for the DWELL FPA was measured to be 80mK at 77K.
Type-II InAs/GaSb superlattice photodiodes for mid-IR (3-5μm) region grown by solid-source
molecular beam epitaxy are reported. Different approaches for realization of high quality interfaces
between compositionally abrupt GaSb and InAs layers during the growth of the SLs are discussed.
Mid wave infrared (&lgr;c~ 4.5 µm at T=300K) P-on-N designs of SLs detectors were developed to
ensure compatibility with most present day readout integrated circuits (ROICs). Variable size diode
arrays were fabricated using standard photolithography technique and hybridized to silicon fanout
chip. The sizes of the detector mesas were varied from 29μm x 29μm to 804μm x 804μm. The
single pixel characterization was undertaken at Santa Barbara Focal Plane. Temperature-dependent
IV measurements revealed dark current density below 1 x 10-8 A/cm2 at 82K and below 2 x 10-5
A/cm2 at 240K. (Vbias = 0V). Dynamic resistance-area product at zero bias was found to be ~ 1 x 105
Ωcm2 at 82K and 0.24 Ωcm2 at 240K. Influence of protective silicon nitride coating on reduction
surface leakage currents of detectors was investigated. We found that rsurface was equal to ~ 3 x 106
Ωcm indicating the proper surface preparation followed by room temperature Si3N4 deposition is
effective in reduction of leakage currents in type-II MWIR InAs/GaSb superlattice photodiodes.
Optimization of various growth parameters for Type-II GaSb (10MLs)/InAs(10MLs) nanoscale superlattices (SL) and
GaSb layers, grown by solid molecular beam epitaxy, has been undertaken. We present optical and structural
characterization for these heterostructures, using high resolution X-ray diffraction (HRXRD), photoluminescence (PL)
and atomic force microscopy (AFM). Optimized parameters were then used for growth of InAs/GaSb SLs photovoltaic
detectors (λcut-off ~5 μm) operating at room temperature. By controlling the nature of interfaces, the in-plane mismatch
between GaSb-buffer layer and SLs can be reduced enabling the growth of active regions up to 3μm. Normal incidence
single pixel photodiodes were fabricated using standard lithography with apertures ranging from 25-300 μm in diameter.
The spectral response from the SLs detector was observed at room temperature. This suggests the potential of the SLs
technology for realizing high operating temperature (HOT) sensors. Responsivity measurements were also undertaken
using a calibrated black body source, 400Hz optical chopper, SR 770 FFT Network signal analyzer and Keithley 428
preamplifier. We obtained current responsivity equal 2.16 A/W at V = -0.3V(300K). The Johnson noise limited D* at
300K was estimated to be 4.6x109 cm·Hz1/2/W at V = -0.3V