N.B.V. Subrahmanyam

More than one order enhancement in peak detectivity (D*) for quantum dot infrared photodetectors implanted with low energy light ions (H−)

In(Ga)As/GaAs-based quantum dot infrared photodetectors (QDIPs) have emerged as one of the most suitable devices for infrared detection. However, quantum dot devices suffer from lower efficiencies due to a low fill-factor (∼20%–25%) of dots. Here, we report a post-growth technique for improving the QDIP performance using low energy light ion (H−) implantation. At high bias, there is evidence of suppression in the field-assisted tunneling component of the dark current. Enhancement in peak detectivity (D*), a measure of the signal-to-noise ratio, by more than one order, from ∼109 to 2.44 × 1010 cm Hz1/2/W was obtained from the implanted devices.

Impact of phosphorus ion implantation on the material and optical properties of InAs/GaAs quantum dots

In this work, we investigated the effects of phosphorus ions implantation on InAs/GaAs QDs by varying the fluences from 8× 1011 to 1×1013 ions/cm2 at a fixed energy of 50 keV. Temperature dependent photoluminescence (PL) study shows a suppression of emission efficiency with the increase of fluence of implanted ions, attributed to the generation of defects/dislocations near around QDs acting as trapping centers for photocarriers. All the implanted samples demonstrated degradation in activation energy from 184 meV (as-grown) to 73 meV (highest fluence sample) indicating weaker carrier confinement in QDs. Implantation also resulted 40 nm blue shift in PL emission wavelength which is caused due to the atomic intermixing between QDs and surrounding materials. Rocking curves plotted from the double crystal X-ray diffraction study, depict a vanishing trend of satellite peaks with the increase of fluence of implanted ions, resulting from the loss of interface sharpness due to interdiffusion.

Improvement in NEDT characteristics of InAs/GaAs quantum dot based 320x256 focal plane array implanted with hydrogen ions

In this work, we demonstrate two times enhancement in NEDT response of InAs/InGaAs/ GaAs dot-in-the-well (DWELL) structure implanted with hydrogen ions of 3 MeV energy and 5×1012 ions/cm2 fluence. Low temperature photoluminescence study shows emission peak at 1130 nm which corresponds to ground state transition between conduction to valence band. PL enhancement is observed in all hydrogen implanted samples indicating the passivation of defects/dislocations in the vicinity of QDs and surrounding layer. The spectral response peak was observed at 5 μm corresponding to the intersubband transition and measured upto 76 K. Next, 320×256 format infrared FPA was fabricated involving multistage lithography, wet etching, metal stack and bump deposition. The NEDT parameter, which represents minimum temperature difference that FPA based camera can resolve, improved from 239 mK( as-grown) to 129 mK ( implanted sample).

Effect of lithium ion implantation on the luminescence properties of InAs/GaAs quantum dots

We have investigated the effect of implantation of Lithium ions of varying energies from 20 keV to 50 keV at fixed dose 2 × 1012 ions/cm2 on InAs/GaAs QDs. Temperature dependent (15K-300K) photoluminescence (PL) study was carried for all samples. Implantation resulted consistent degradation in PL efficiency with rise in energy of ions. The same trend was also observed while varying the fluence at fixed energy. Suppression in PL intensity might be due to creation of defects/damage profile in the vicinity of the QDs which act as trapping centers for photocarriers. Implantation also resulted in decrease of activation energies from 230 meV (as-grown) to 35 meV (50 keV) indicating reduced carriers confinement in QDs. The 50 keV sample demonstrated the mild red shift in PL spectra which is probably originated from atomic interdiffussion between dots and barrier layer caused by local heat generation.

Effect of high energy proton implantation on the device characteristics of InAlGaAs-capped InGaAs/GaAs quantum dot based infrared photodetectors

Self-assembled In(Ga)As/GaAs quantum dot infrared photodetectors (QDIPs) have promising applications in the midwavelength infrared and long-wavelength infrared regions for various defense and space application purposes. It has been demonstrated that the performance of QDIPs has improved significantly by using architectures such as dots-in-awell, different combinational capping or post growth treatment with high energy hydrogen ions. In this work, we enhanced the electrical properties InGaAs/GaAs using high energy proton implantation. Irradiation with proton resulted suppression in field assisted tunnelling of dark current by three orders for implanted devices. Photoluminescence (PL) enhancement was observed up to certain dose of protons due to eradication of as-grown defects and non radiative recombination centers. In addition, peak detectivity (D*) increased up to two orders of magnitude from 6.1 x108 to 1.0 × 1010 cm-Hz1/2/W for all implanted devices.

Influence of low energy H- ion implantation on the electrical and material properties of quaternary alloy (In0.21Al0.21Ga0.58As) capped InAs/GaAs n-i-n QDIPs

The effect of low energy H– ions implantation on the InAs/GaAs quantum dot infrared photodetectors had been studied. Light ion implantation was found to be an effective post growth technique which helped dark current density suppression by four orders in the implanted devices. In this study we had mainly concentrated on determining how the defect-related material and structural changes had an impact on dark current density reduction for InAs/GaAs quantum dot infrared photodetectors.

Reduction of dark current density by five orders at high bias and enhanced multicolour photo response at low bias for quaternary alloy capped InGaAs/ GaAs QDIPs, when implanted with low-energy light (H-) ions

Considering the importance of In(Ga)As/GaAs QDIPs, a post-growth method had been developed for enhancing QDIP characteristics using low energy light ion (H-) implantation. Dark current density was reduced by about five orders for the implanted devices due to the reduction in field assisted tunneling process for dark current generation, even at a very high bias of operation. Stronger multicolor mid wavelength photo response (~5.6 µm) was achieved at a very low bias of operation for the implanted device.