Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
A. G. U. Perera - Chair
Electrical and optical characterizations of heterostructures and thin ﬁlms based on group III-V compound semiconductors are presented. Optical properties of GaMnN thin ﬁlms grown by Metalorganic Chemical Vapor Deposition (MOCVD) on GaN/Sapphire templates were investigated using IR reﬂection spectroscopy. Experimental reﬂection spectra were ﬁtted using a non - linear ﬁtting algorithm, and the high frequency dielectric constant (ε∞), optical phonon frequencies of E1(TO) and E1(LO), and their oscillator strengths (S) and broadening constants (Γ) were obtained for GaMnN thin ﬁlms with different Mn fraction. The high frequency dielectric constant (ε∞) of InN thin ﬁlms grown by the high pressure chemical vapor deposition (HPCVD) method was also investigated by IR reﬂection spectroscopy and the average was found to vary between 7.0 - 8.6. The mobility of free carriers in InN thin ﬁlms was calculated using the damping constant of the plasma oscillator. The terahertz detection capability of n-type GaAs/AlGaAs Heterojunction Interfacial Workfunction Internal Photoemission (HEIWIP) structures was demonstrated. A threshold frequency of 3.2 THz (93 µm) with a peak responsivity of 6.5 A/W at 7.1 THz was obtained using a 0.7 µm thick 1E18 cm−3 n - type doped GaAs emitter layer and a 1 µm thick undoped Al(0.04)Ga(0.96)As barrier layer. Using n - type doped GaAs emitter layers, the possibility of obtaining small workfunctions (∆) required for terahertz detectors has been successfully demonstrated. In addition, the possibility of using GaN (GaMnN) and InN materials for terahertz detection was investigated and a possible GaN base terahertz detector design is presented. The non - linear behavior of the Inter Pulse Time Intervals (IPTI) of neuron - like electric pulses triggered externally in a GaAs/InGaAs Multi Quantum Well (MQW) structure at low temperature (~10 K) was investigated. It was found that a grouping behavior of IPTIs exists at slow triggering pulse rates. Furthermore, the calculated correlation dimension reveals that the dimensionality of the system is higher than the average dimension found in most of the natural systems. Finally, an investigation of terahertz radiation efect on biological system is reported.
Weerasekara, Aruna Bandara, "Electrical and Optical Characterization of Group III-V Heterostructures with Emphasis on Terahertz Devices" (2007). Physics and Astronomy Dissertations. Paper 16.