NDTnet 1998 Aug, Vol.3 No.8

Abstract

The methods for testing of impurity atoms and defects of technological and radiation nature in single-crystal impurity semiconductors like Ge and Si have been developed, basing on application of the phenomenon of low-temperature relaxation of quasiequilibrium impurity or hopping conductance, induced by ionizing optical radiation. By the example of single-crystal B-doped Si it was experimentally shown, that these methods can be used to test concentration of interstitial B and remaining P impurity after crystal fabricating and treatment with electrons of high energy. At concentration of a doping impurity (boron) in the range 10¹⁵- 10¹⁷ cm ^-3 the concentration of electrically active compensating impurities and defects can be estimated with an error (3-5)%, though their contentin Si is 10³ - 10⁵ times less compared with concentration of a doping impurity.Under low temperature impurity atoms in Ge and Si become effective traps for charge carriers, and capture possibility significantly exceeds the possibility of recombination. Under such conditions on exposure of a semiconductor with optical radiation with photon energy, enough to generate electron-hole pairs, one can observe induced long-term nonequilibrium conductance. If a hopping conductance prevails in an impurity zone, then induced conductance appears in a form of negative photoconductivity with a characteristic time of relaxation from several seconds to several tens of minutes. The relaxation process characteristics greatly depend on an impurity type and impurity atoms position in a semiconductor lattice. So by definition of impurity atoms and defects contributions into the relaxation process one can control their characteristics and relative concentration. For realization of methods it is necessary to have two ohmic contacts, connected to a tested semiconductor region. Development of effective algorithms to identify parameters of relaxation models allows to develop a reliable methods for testing of compensating impurities and defect states in impurity semiconductors (Patent RU 2025827 C1). The methods can be realized, using apparatus, consisting of a small-size cryostat of a submerged type, transport He vessel CTT-40 and a measuring interface, controlled by IBM computer PC/AT.

Principal technical characteristics for B doped Si:


• Sensitivity of compensation degree definition (3-5)% in the range from 0.001 to 0.00001 for majority impurity (B) concentration in the range from 2 10⁶ to 8 10¹⁶ cm^-3.
  
• Sensitivity of residual P concentration definition and interstitial boron - (2-4)10¹⁰ cm^-3.

  These methods can be used in electronic and space industries for testing and quality control of semiconductors and semiconducting devices, made on the basis of doped Si and Ge, particularly, in impurity IR detectors, used for detection of slightly heated objects in space.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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