Location
Radisson Resort at the Port, Convention Center, Jamaica Room
Start Date
27-4-1999 2:00 PM
Description
We consider the II-VI narrow gap semiconducting alloys Hg(1-x)Cd(x)Te, Hg(1-x)Zn(x)Te, Hg(1-x)Zn(x)Se, for which empirical equations exist that give each alloy’s forbidden energy band gap Eg(x) as a function of its stoichiometry as characterized by the value x . These materials are important to NASA for two reasons. They are useful for making infrared detectors, and they are best grown in microgravity to optimize their uniformity. The equations can be inverted to yield the stoichiometry parameter x provided that the value of Eg can be determined experimentally, for example, by optical absorption measurements. We have investigated an alternative method, which should yield appreciably better spatial resolution, in which scanning tunneling optical spectroscopy (STOS) is used to measure the enhancement of the current that is due to photoexcitation of carriers at the tunneling junction in an STM.
We present a simplified working model for low temperature calculations of STOS. Our major conclusions are: (a) for the degenerate case, knowledge of ND - NA (donor density minus the acceptor density) can be used to deduce the true band gap from the apparent band gap, (b) the low temperature tunneling current may have a sharper onset, depending on the diffusion length, at the band gap than does the optical absorption, and (c) our simplified formulation allows for quick, straightforward evaluation of many different cases and is in essential agreement with more detailed analysis.
Paper Session I-B - Characterizing Space-Grown Degenerate Narrow Gap Semiconductors by Scanning Tunneling Optical Spectroscopy
Radisson Resort at the Port, Convention Center, Jamaica Room
We consider the II-VI narrow gap semiconducting alloys Hg(1-x)Cd(x)Te, Hg(1-x)Zn(x)Te, Hg(1-x)Zn(x)Se, for which empirical equations exist that give each alloy’s forbidden energy band gap Eg(x) as a function of its stoichiometry as characterized by the value x . These materials are important to NASA for two reasons. They are useful for making infrared detectors, and they are best grown in microgravity to optimize their uniformity. The equations can be inverted to yield the stoichiometry parameter x provided that the value of Eg can be determined experimentally, for example, by optical absorption measurements. We have investigated an alternative method, which should yield appreciably better spatial resolution, in which scanning tunneling optical spectroscopy (STOS) is used to measure the enhancement of the current that is due to photoexcitation of carriers at the tunneling junction in an STM.
We present a simplified working model for low temperature calculations of STOS. Our major conclusions are: (a) for the degenerate case, knowledge of ND - NA (donor density minus the acceptor density) can be used to deduce the true band gap from the apparent band gap, (b) the low temperature tunneling current may have a sharper onset, depending on the diffusion length, at the band gap than does the optical absorption, and (c) our simplified formulation allows for quick, straightforward evaluation of many different cases and is in essential agreement with more detailed analysis.
