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HL: Halbleiterphysik

HL 53: Heterostrukturen

HL 53.7: Talk

Friday, March 28, 2003, 13:15–13:30, BEY/118

Determination of small conduction band offsets in highly strained heterosystems — •Mathias Ziegler, Mykhaylo Semtsiv, and Ted Masselink — Humboldt University Berlin, Invalidenstr. 110, 10115 Berlin, Germany

The conduction band offset (CBO) in heterostructures is often determined by measuring thermionic emission current in n-i-n structures as a function of temperature and voltage. The total resistance of such structures is determined by the mesa size, thickness of intrinsic layer, and the CBO. To obtain a reliable value, the intrinsic contribution to the resistance should be significantly larger than the resistance of the ohmic contacts. In the case of a highly strained barrier layer, its thickness is limited, resulting in additional tunneling current. When the CBO is small, the determination of its value becomes especially challenging. The intrinsic resistance can be increased, however, by stacking a number of strained barriers with thick n-type spacer layers between them. An additional advantage of the use of such a superlattice is the accurate verification of composition and thickness parameters via X-ray rocking curves modeling. We demonstrate the utility of this approach, measuring the CBO of In_0.32Ga_0.68P relatively to relaxed GaAs. The data fit the thermionic emission model in the 300 K - 240 K temperature range very well and the CBO is determined to be 80 meV. A similar experiment using a single barrier in the same materials does not lead to consistent result.

This work was supported by the Deutsche Forschungsgemeinschaft within Forschergruppe 344.