Achyut K. Dutta

Novel multicolor photodetectors for short- and long-distance optical communication

Multicolor (a.k.a. broadband) photodetector having a detection capability ranging from near ultra-violet to infrared can be useful as a common detector for various applications such as optical communication and optical interconnects etc. The capability of using single detector in receiver system for optical communication covering both data and transport systems, not only makes the total system cost lower, but it also makes easier the system vendors to reduce the inventory. We proposed detector having the detection capability ranging from 350 nm to 2000 nm, wavelengths that covers all optical communication wavelengths application. This invited paper has two-fold objectives: (a) provide a comprehensive overview of conventional photo detectors and their types, being used in todays optical communication and (b) introduce a development of broadband photodetector which authors pioneered. The features of proposed broadband detector are simple structure, low-cost, high quantum efficiency, high sensitivity, and high speed. Performance results will be presented along with its possible applications.

High-efficiency solar cells based on micro-nano scale structures

Higher efficiency solar cells are required to reduce solar array mass, stowed volume, and cost for numerous commercial and military applications. Conventional solar cell made of thin-film or crystal-Si (c-Si) or other thin films have limited conversion efficiency of 10 to 20% with the cost of

Ultra-high sensitivity gas sensors based on GaN HEMT structures

3-

Novel optical nano-sensor for biomolecule and chemical agents detection

5/Wp. Current state-of-the-art crystalline multijunction solar cells are ~30 % efficient with the cost of

Design and simulation of infrared energy harvesting devices

30 to

Floating gate based ultra-high-sensitivity two-terminal AlGaN/GaN HEMT hydrogen sensor

40 /Wp. Increasing conversion efficiency of > 30% will enable to reduce the cost <

Novel nano-sensor for biomedical and industrial applications

1/Wp and useful for various power platforms supporting mobile wireless, laptop, tent applications. Solar cell comprises with three dimensional blocks are shown to be higher conversion-efficiency than standard flat-type solar cell. Incorporating nano-scaled blocks in solar cell structures are shown to be increased performances due to (i) increase of the surface area to volume ratio, (ii) brining the junction closer to the carrier generation region which eliminate the carrier recombination , (iii) absorption of all incident photon flux, and (iv) broadening the absorption spectrum. Our activities on next generation high performance solar cells based on micro-nano scaled structures and various material systems will be presented. Details fabrication process of micro-nano scaled solar cell friendly to mass scale manufacturing will be also be described. We have achieved more than 20x optical performance enhancement for the solar cell based on micro-scaled structures, than that of flat-type (standard) solar cell, fabricated on the same Si substrate and same process. Simulation results showed that significant improvement in conversion efficiency more than 30% is possible for even c-Si solar cell based on the micro-nano scaled structures. Key issues and challenges for bringing it to the manufacturing will be discussed.

Imaging beyond human vision

This paper presents simulation of GaN high electron mobility transistor (HEMT) based device structures for the detection of toxic and hazardous gases like carbon monooxide (CO) and hydrogen (H2), respectively. AlGaN/GaN heterostructures show large potential as sensors due to the presence of 2-dimensional electron gas (2-DEG) at the heterointerface. Due to widebandgap material properties, GaN based devices are highly suitable for extreme-environment applications. The sensors are proposed selective towards specific targets by the two different gate structures. The simulated AlGaN/GaN based HEMT with Pt/AlGaN Schottky gate structure can detect hydrogen gas with the concentrations as low as ppb level and with the linear output variations from ∼ ppb to 100 ppm level. A new gate structure based on nanocrystalline stannic oxide (α-SnO2) layer for the selective and sensitive detection of CO gas is proposed. We report that the AlGaN/GaN HEMT structure with Pt/α-SnO2/AlGaN Metal-Oxide-Semiconductor (MOS) gate can be used to detect sub-ppm level of CO with the linear response upto 500 ppm.

Ultra-high sensitivity CO-sensor based on nanocrystalline metal oxide gate AlGaN/GaN heterostructure

A novel photonic band-gap (PBG) based nano-sensor is proposed for biomolecule gas/chemical agents, and various industrial gas detections. The proposed sensor is based on the plannar waveguide formed by utilizing the PBG. Sensor structure is optimized for a fixed wavelength of light and fixed recpetor. Biomolecule gas adsorbed/interact with the receptor, cause changes in refractive index, which thereby reduces the output optical power. Type of gas and its density in the air can be known from the changes in output optical power, compared with no-gas (reference) adsorption. The proposed sensor can able to detect the fixed gas in several tens of parts-per-billion. We will present detailed simulation and the results of this proposed sensor for various biomolecule gas/chemical agents and also industrial gases. In addition to biomolecule gas/chemical agents detection, the proposed nano-sensor is also expected to be useful for various applications for example in clinical diagnostic system to measure the specific cell or DNA.

Ultraviolet photodetectors directly integrated on CMOS using low-temperature ZnO-based nanowire techniques

Despite a recent focus in developing energy harvesting technologies from a variety of sources, no work has been done in capturing blackbody radiation from the surrounding environment. This work aims to extend semiconductor-based solar energy harvesting into the infrared (IR) range of the electromagnetic spectrum so as to take advantage of this blackbody radiation. We have investigated the use of mercury cadmium telluride (HgCdTe) p-n junction devices in order to achieve this goal. A device simulation tool, named MCT-SIM, was developed in order to obtain the photovoltaic characteristics of P+/N-/N+ structures exposed to blackbody radiation and an applied voltage bias. An IR energy harvesting system was developed and evaluated with the use of this tool. When this system is exposed to blackbody radiation at a temperature of 300 K, it generates a series-limited photocurrent of 28.115 mA/cm2; this value can be increased through further optimization. Subsequent analysis shows that performance limitations of this system are due to the presence of a large intrinsic carrier concentration and associated Auger effects within the absorbing layer of HgCdTe.