Polarization-engineering in group III-nitride heterostructures: New opportunities for device design
نویسندگان
چکیده
The role of spontaneous and piezoelectric polarization in III–V nitride heterostructure devices is discussed. Problems as well as opportunities in incorporating polarization in abrupt and graded heterojunctions composed of binary, ternary, and quaternary nitrides are outlined. 1 Introduction Spontaneous polarization exists along the (0001) (metal-polar) and ð0001Þ (N-polar) directions of wurtzite III–V nitride semiconductor crystals. Strain-induced piezoelectric polarization can either add to, or subtract from the spontaneous polarization in heterostruc-tures based on the composition and polarity. At a sharp heterojunction, the discontinuity in polarization leads to the appearance of an immobile polarization sheet charge (unit: C/cm 2) of density:
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