Design And Fabrication Of Normal Incidence P-type SiGe/Si Quantum Well Infrared Photodetector

Quantum well infrared photodetectors (QWIPs) offer numerous potential applications in defense, industry and medicine. For conventional n-type QWIPs, special optical couplers such as gratings are always required to detect normal incidence because the transition is forbidden by the quantum mechanical selection rules. Whereas, the p-type QWIPs are sensitive to normally incident radiation and have lower dark current than n-type QWIPs, which makes them attractive for normal incidence detection. Among those, p-type SiGe/Si QWIP is of particular interest, because of its compatibility with the well-established Si microelectronics technology, matching well with Si readout circuitry, including monolithic integration with Si based photoelectric device. All of those make p-type QWIPs based on this material worth pursing.The studies on this subject were carried out in the present thesis as follows:(1) Energy band designs for p-type strain SiGe/Si QWIP are discussed byusing the six-band k·p theory, the valence band structure of which werecalculated versus different well width or Ge concentrations in the quantum well. Then we discussed the energy designs based on the bound-to-quasibound transitions. Moreover, a novel p-type tensile strained SiGe/Si QWIP is proposed. It shows that the light-hole state with small effective mass becomes the ground state in the tensile strained quantum wells, which is expected to have larger absorption coefficient and better transport characteristics than those of conventional unstrained or compressive strained p-type QWIPs. Those researches provided a theoretical basis for energy band designs of p-type strained SiGe/Si QWIP and the growth of device material.(2) High quality SiGe/Si MQWs for QWIPs is successfully grown by DC-UHV/CVD. The infrared absorption spectra of the SiGe/Si MQWs with broadband absorption between 3-6μm were measured using LT-FTIR. The peak at 4pm is due to intersubband absorption between the heavy hole ground and continuum states.(3) The technologies of fabricating SiGe/Si QWIP were investigated, including the conditions related to photolithography, RIE and etching process. Finally, p-type SiGe/Si QWIPs have been successfully fabricated. The photocurrent spectra for normal incidence measured at 300k show two peaks at 1.08μm and 1.51μm, which may be due to the interband transitions of silicon, strained SiGe and the transitions related with band-tail.