Heterojunction interface formation: Si on Ge, GaAs, and CdS

Abstract

We used photoemission spectroscopy with synchrotron radiation to investigate the formation and the microscopic properties of interfaces between semiconducting substrates and Si overlayers deposited by electron bombardment. The main goal of the experiment was to measure the valence band discontinuity in these systems and test the limits of the discontinuity transitivity rule predicted by all ‘‘linear’’ models. This rule could be tested by combining our present data on Si overlayers and previous data on Ge overlayers on Si, GaAs, and CdS. We found that the rule is valid for the above interfaces only within an accuracy of a few tenths of an electron volt. Our results are in agreement with recent evidence that the Harrison LCAO approach, one of the ‘‘linear’’ models, predicts the valence band discontinuities with an accuracy of the order of ∼0.25 eV.

The Role of Photoemission Spectroscopies in Heterojunction Research

“…14.2(a)) we see the scheme of a photoemission experiment in which an electron absorbs the energy of an incoming photon, hn, is emitted into the vacuum, and is then captured and analyzeddmeasuring in particular its energy. Note that, once DE v is known, the conduction-band discontinuity is simply given by: Figure 14.3 shows a good example [8] of this approach: the photoelectron energy distribution of the CdSeSi heterojunction interface. During a photoelectron emission process, the energy of the involved electron is first augmented by an amount equal to the energy of the absorbed photon, hn.…”

“…Figure 14.2(b) illustrates a photoemission experiment for the semiconductor A only. Early experiments of this type [1,3,8] practically transformed band discontinuities from merely theoretical notions only indirectly measurable to very concrete and tangible entities, relatively easy to visualize and study. Some of the excited electrons reach the vacuum without losing any energy.…”

Can photoemission measure valence-band discontinuities?

“…2 an example of the complications produced by chemical reactions at the Si/GaAs( 110) interface. 7 The As 3d core level exhibits more subtle reactions which would introduce an error of ~ 0.1 e V in the opposite sign to that of the Ga. We should also note that for surface sensitive photoemission, it is also important to include the contributions from the surface shifted components. In the figure we present the surface sensitive, core level photoemission spectra of all components of the heterojunction as a function of increasing Si coverage.…”

Bandgap Engineering of Bilayer Ge/CdS Thin Films via Interlayer Diffusion under Different Annealing Temperatures

“…The ability to engineer a bandgap of a multilayer thin-film solar cell is a technological milestone corroborated by the widespread research efforts over the past few decades. Many efforts have been put by the scientists to develop cascaded structures of intrinsic (Si and Ge) and extrinsic semiconductor compounds (metal chalcogenides [9][10][11] and perovskites [12,13]). However, II-VI semiconductors have been rather less explored and needed further attention.…”