On the determination of the interface density of states

One of the most interesting aspects of amorphous semiconductor multilayers is their application in studying the interfaces between different a-Si:H based alloys, because of the great number of interfaces that a multilayer structure can contain. There are several magnitudes, such as the additional hydrogen content at interfaces [1,2] or the density of states (DOS) per interface [3-7] that can be estimated from measurements of series of multilayers with different geometries and number of interfaces. In particular, the DOS per interface is a valuable parameter used to define the optoelectronical quality of interfaces. One of the most suitable techniques for the measurement of DOS is photothermal deflection spectroscopy (PDS). However, the use of PDS to determine the DOS per interface requires accurate determination of the surface DOS (i.e. the DOS at air/multilayer and multilayer/substrate interfaces) and the strong assumption of a constant surface DOS in spite of the geometry of the multilayer [4]. Other complications can arise from the more defective material in the multilayer (usually the alloy), whose contribution to the measured total DOS can obscure the smaller contribution from the DOS at interfaces.