Heterojunction band offset engineering

The physics and technology of a relatively new, short‐time, thermal processing technique, namely rapid isothermal processing (RIP), based on incoherent sources of light for the fabrication of semiconductor devices and circuits, are reviewed in this paper. Low‐cost, minimum overall thermal budget, low‐power consumption, and high throughput are some of the attractive features of RIP. The discussion of RIP, in the context of other thermal processes, history, operating principles, different types of RIP systems, various applications of RIP using single processing steps, and novel applications of RIP, including in situ processing and multistep processing, is described in detail. Current trends are in the direction of RIP‐dominated silicon integrated circuit fabrication technology that can lead to the development of the most advanced three‐dimensional integrated circuits suitable for applications such as parallel processing and radiation hardening. RIP is not only a superior alternative to furnace processing, but it is also the only way to perform certain crucial steps in the processing of compound semiconductor devices such as high‐mobility transistors, resonant tunneling devices, and high‐efficiency solar cells. Development of more accurate temperature measurement techniques and theoretical studies of heat transfer and other fundamental processes are needed. Dedicated equipment designed for a specific task coupled with in situ processing capabilities will dominate the future direction of RIP.

Rapid isothermal processing

Foreword.- Introduction.- Status of heterojunction solar cell R&D.- Basic features of Heterojunctions illustrated by selected experimental methods and results.- Deposition methods of thin film silicon.- Electronic properties of ultrathin a-Si:H layers and the a-Si:H/c-Si interface.- Degradation of (bulk and thin film) a-Si and interface passivation.- Photoluminescence and electroluminescence for a Si:H/c Si device and interface characterization.- Deposition and properties of transparent conductive oxides.- Metallization and formation of contacts.- Electrical and optical characterization of a-Si:H/c Si cells.- Wet-chemical pre-treatment of c Si for a-Si:H/c-Si heterojunctions.- Theory of heterojunctions and the determination of band offsets from electrical measurements.- Modeling and simulation of a Si:H/c Si cells.- Surface passivation using ALD Al2O3.- Introduction to AFORS-HET.- Hands-on experience with simulation tools.- a-Si:H/c-Si heterojunction and other high efficiency solar cells: a comparison.- Rear contact cells.- Progress in systematic industrialization of Hetero-Junction-based Solar Cell technology.

Physics and Technology of Amorphous-Crystalline Heterostructure Silicon Solar Cells

Structures and electronic transport on silicon surfaces

Publisher Summary This chapter presents an overview of several theoretical approaches and experimental measurement techniques for determining band offset values and discuss the experimental and theoretical data reported for a number of specific heterojunction systems. It also evaluates the credibility and accuracy of the experimental measurements and provides a tabulation of reliable band offset values for as many heterojunctions as possible. Among the most important physical parameters for a given heterojunction system are the conduction- and valence-band offsets; indeed, the quality and even the feasibility of heterojunction device concepts often depend crucially on the values of these band offsets. The band offset is defined simply as the discontinuity in the band edge at the interface between two semiconductors. A number of current theories seem to yield band offset values in reasonable agreement with experiment, even though the physical ideas underlying these theories can be quite different. These ideas include electron affinities, Schottky barrier heights, bulk band structures on the same energy scale, and the definition of effective midgap energies corresponding to charge neutrality for each bulk constituent.

Band Offsets in Semiconductor Heterojunctions

We discuss two recent results on the microscopic nature and control of the band lineup at semiconductor-semiconductor interfaces. First, we identified a correlation between measured heterojunction band discontinuities and Schottky barrier heights of the corresponding semiconductors, as predicted by several theoretical models. Second, we found that ultrathin metal intralayers modify the band lineup of polar interfaces by several tenths of an electron volt. At least in principle, this degree of freedom can be exploited to tailor heterojunction devices.

Understanding and controlling heterojunction band discontinuities

We extended our empirical method for estimating heterojunction band discontinuities to systems containing AlAs. The necessary data were provided by a synchrotron‐radiation photoemission study of the AlAs‐Ge interface formation. Our results suggest that the ‘‘15%–85%’’ rule deduced for Ga1−xAlxAs‐GaAs cannot be extrapolated to AlAs‐GaAs.

Valence-band discontinuities at AlAs-based heterojunction interfaces

The interactions of the reactive metals Al and In with both cleaved and sputtered p‐type Hg1−xCdxTe surfaces have been investigated using synchrotron radiation‐induced ultraviolet photoelectron spectroscopy. The sputtered surfaces are depleted of a fraction of their Hg (∼25% and ∼40% for x=0.21 and x=0.28 material, respectively, relative to the Hg found on the corresponding cleaved surfaces) and are more inverted than the cleaved surfaces with the Fermi level higher in the conduction band. During metal deposition, the cleaved and sputtered surfaces behave similarly: in the initial stages, the metal reacts with the HgTe alloy component to form a metal telluride and Hg, which leaves the surface region. At the same time, the inverted surface becomes more degenerate. After the metal has reacted with all the available HgTe within a certain surface region, an unreacted metallic film grows on the surface. Such identical behavior of the two types of surfaces is explained by the large difference in thermodynamic s...

Deposition of the reactive metals Al and In onto sputtered and cleaved Hg1−xCdxTe surfaces

Note: Univ wisconsin,dept phys,madison,wi 53706. montana state univ,dept phys,bozeman,mt 59717. Kelly, mk, univ wisconsin,ctr synchrotron radiat,madison,wi 53706.ISI Document Delivery No.: APH08 Reference LSE-ARTICLE-1985-007 Record created on 2006-10-03, modified on 2017-05-12

High-Resolution Electron-Energy Loss as a Probe of the Si-Al Schottky-Barrier Formation Process

Intermetallic yttrium-iron compounds do have a strong affinity to hydrogen. Exposure to ${\mathrm{H}}_{2}$ at 300 K leads to a hydrogen-induced state at 5.3 eV below ${E}_{F}$ and a strong reduction of d-like states at ${E}_{F}$. For higher ${\mathrm{H}}_{2}$ exposures at 700 K, these hydrides undergo a metal-to-semiconductor transition with an energy gap ${E}_{0}$=0.3\ifmmode\pm\else\textpm\fi{}0.1 eV. In addition to the lowering of d-like states at ${E}_{F}$, a second ${\mathrm{H}}_{2}$-induced structure appears at 10 eV.

E. Colavita

Papers

Understanding and controlling heterojunction band discontinuities

Valence-band discontinuities at AlAs-based heterojunction interfaces

Deposition of the reactive metals Al and In onto sputtered and cleaved Hg1−xCdxTe surfaces

High-Resolution Electron-Energy Loss as a Probe of the Si-Al Schottky-Barrier Formation Process

Photoemission study of the hydrogenation of the intermetallic compounds YFe 3 and YFe 2