OSE Dissertation Defense with Mr. Md Mottaleb Hossain, Ph.D. Candidate
Posted: November 27, 2018
Date: Wednesday, November 28, 2018
Time: 10:00 AM
Location: CHTM, Room 146
Map to CHTM:
Parking passes are available at the receptionist desk. The CHTM building is equipped with ADA accommodations as well as parking spaces.
Future smart-lighting systems are expected to deliver adaptively color-tunable and high-quality lighting that is energy efficient while also offering integrated visible-light wireless communication services. To enable these systems at a commercial level, inexpensive and fast sensors with spectral-sensing capability are required. CMOS-compatible silicon avalanche photodiodes (APDs) can be an excellent fit to this problem due to their excellent sensitivity, high speeds and cost effectiveness; however, color sensing is a challenge without resorting to expensive spectral filters, as done in commercially. To address this challenge, we have recently designed and modeled a novel CMOS-compatible dual-junction APD. The device outputs two photocurrents simultaneously, one for each junction, and each junction is controlled independently via a bias voltage so that each photocurrent can exhibit its own avalanche amplification factors and sensitivity. What is unique here is that each APD responds differently to different wavelengths because of (1) the wavelength-dependent nature of the light-absorption profile in the device, and (2) the dependence of the avalanche multiplication process on the location of photon absorptions (and hence on wavelength). The idea is to produce a series of photocurrent pairs, at judiciously prescribed pairs of biases for each acquisition, which would contain sufficient spectral information about the light as well as its intensity, which can be extracted from the data via an algorithm. Modeling shows that we can ideally use a pair of biases to detect the color and intensity within 10 nm spectral resolution in the 450-650 nm wavelength range using a spectral sensing algorithm with maximum likelihood (ML) estimator. We propose to develop a programmable, inexpensive (CMOS compatible) dual-junction silicon APD that outputs the intensity and spectrum of the sensed illumination that addresses the needs of smart lighting without the use of any spectral filters. The efforts include: (1) the computation of the mean gain, excess noise factor and avalanche breakdown voltage for the dual APD as a function of bias and wavelength, (2) development of an exact analytical formula for excess noise factor under mixed injection, and (3) development of an exhaustive computation of the ML estimates of the intensity and spectral profile. The ML computations include an exhaustive search of a multidimensional space of wavelength and intensity values.