On the development of a far-infrared bolometric detector using a 2DEG as the absorbing medium

This thesis describes the development of a far-infrared bolometric detector using a two-dimensional electron gas (2DEG) as the detecting medium. The 2DEG is formed at a AlGaAs/GaAs heterojunction made of layers of undoped GaAs and AlGaAs and highly doped (5 x lO126 3) AlGaAs. A 2DEG layer grown in this way in a molecular beam epitaxy (MBE) system is generally within 100 nm of the surface of the wafer and is subsequently patterned by etching away the surrounding wafer material and leaving a mesa containing the buried 2DEG. Ohmic contact to the 2DEG is achieved either through a diffusion of charge carriers into the contact region. Using a 2DEG as the absorbing medium in bolometers will yield detectors that are fast, sensitive, and frequency selective. The low electron densities in 2DEGs (1011 cm-2) allow large-area devices with extremely low thermal conductance between the electrons and the semiconductor lattice (e.g. Appleyard, et al. 1). The fast time constant (on the order of 1 ps) of the electron relaxation time in the 2DEG would allow for very high bandwidth spectroscopy. This thesis presents an overview of the use of 2DEG bolometers and a detailed study of their properties relevant for use as THz HEBs or CEBs. Chapter 1 briefly outlines the importance of Terahertz astronomy. Chapter 2 presents an introduction to bolometer theory. Chapter 3 provides a description of the electrical, thermal, and magnetic properties of 2DEGs. Chapter 4 outlines the equations governing the operation of 2DEG HEBs and CEBs and contains computer-simulated data. Chapter 5 describes our device fabrication, testing methods, and gives the results of our measurements. Finally, this thesis concludes with a discussion of the results of the tests and possible interpretations in terms of different physical models for electron-photon interactions in the 2DEG