Characterization of semiconductor materials and devices using acoustoelectric voltage measurement

Abstract

During the past 20–25 years, the nondestructive surface acoustic wave (SAW) measurement technique has been developed and used to characterize the electrical properties of semiconductor materials and devices. Important semiconductor parameters such as carrier density, type and mobility, interface and fixed oxide charge densities, deep-level cross section and activation energy, and excess carrier generation and recombination lifetimes are all determined using SAW. In the majority of these experiments, separate medium structure is used where SAW is generated at the surface of a piezoelectric substrate like LiNbO3. SAW in the piezoelectric materials is accompanied by a decaying electric field which interacts with the free carriers of a semiconductor placed nearby. The spatial resolution that is usually achieved in these measurements is on the order of the SAW wavelength or the extrinsic Debye length, whichever is shorter. Variety of semiconductors are characterized using SAW including: silicon, GaAs, AlxGa1−xAs, InAs, GaP, HgxCd1−xTe, CdTe, InP, CdS, and InAs. More recently, high Tc ceramic superconductors have also been studied. The most important aspect of the SAW technique is that it is nondestructive and it has very high sensitivity in studying high resistivity materials. Here, we present a review of the SAW technique discussing its application in quantitative characterization of semiconductor materials and devices.