Field-effect transistors as tunable infrared detectors

Two problems are discussed in this thesis. In Part I, we present a theory of tun- able infrared response in metal-oxide-semiconductor field-effect transistor. Multipole plasmons are localized collective electronic oscillations which arise from a nonuniform density of electrons. We investigate whether multipole plasmons in semiconductor quantum well structures can be used as linear or nonlinear detectors of infrared ra- diation. The frequencies of these detectors can be tuned using a gate voltage. We study the response of the MOSFET to static and time-dependent electric field applied perpendicular to its interface metal-semiconductor. A time-dependent local density approximation is used to calculate the optical response. To achieve our goal, we calculated the linear α(ω) and the second-order β(ω) polarizability as function of the frequency of the applied electric field. If the separation between the lowest subbands is δ, then intersubband transitions require a photon energy ħω₁ = δ for one photon transitions, and 2ħω = δ for two photon transitions. The linear polarizability α(ω) has resonance at frequencies near ω₁, while the second-order polarizability β(ω) has resonance at frequencies near ω₂. There are some plots of the polarizabilities to show their resonant frequencies in function of the change in the gate voltage. In Part II, we calculated the ground-state energy of the metallic hydrogen and potassium by Hartree-Fock variational method.