ABSTRACT
The advent of commercially available field emission transmission electron microscopes has seen the emergence of new techniques for high spatial resolution analysis of interfaces and boundaries. This chapter examines an asymmetric spacer layer tunnel diode (ASPAT) using two forms of electron holography to elucidate the structure and composition of a thin AlAs quantum well buried within a GaAs substrate. The sensitivity of the holographic methods shows how such wells can be examined with high accuracy. The ASPAT diode manages to combine a range of desired properties that include wide dynamic range, low excess noise and low sensitivity to ambient temperature. The chapter utilizes two forms of electron holography. The first is off-axis electron holography in which an electron biprism is used to split a coherent wavefront, allowing interference fringes to be recorded on a charge coupled detector camera. The second method is in-line electron holography, in which a series of images are taken at successive defocus settings.
