CdS-Metal Contact at Higher Current Densities

2015

Annalen der Physik

When the electron density decreases stronger than linearly with the electric field in photoconductive CdS due to field quenching, high-field domains must occur that remain attached to either the cathode or anode in slit electrode geometry with blocking cathodes. These Böer domains 1 are easily seen by their shift in optical absorption due to the Franz-Keldysh effect and offer unique opportunities to analyze field dependent parameters within the range of constant electron density and electric field, such as the carrier density or mobility as a function of the field, and give information of the light dependent work function. They also provide insight why a 200Å thick cover layer of CdS on top of a CdTe solar cell increases its efficiency from 8 to 16% . The behavior of these Böer domains escapes conventional current voltage analyses except for their visual observation, while other high-field domains with their current fluctuations or oscillations are easily observed and are the subjects of thousands of publications and many books. In this review we will exclude detailed discussion of dynamic domains, but include some new specifics that help to understand the mechanisms of the Böer domains and their applications. Only properties at low optical excitation intensities are discussed that exclude Joules heating. Within the p-type regime of the anode-adjacent domain extremely steep electronic quenching signal becomes visible that could signalize an intrinsic donor level slightly above the middle of the band gap that may be responsible for not allowing CdS to ever become ptype by doping.

Section: The Effective Work Functionmentioning

confidence: 58%

Section: Massive Hole Injection From Au Anode At 125 Kv/cm To Maintaimentioning

confidence: 99%

The importance of gold‐electrode‐adjacent stationary high‐field Böer domains for the photoconductivity of CdS

2015

Annalen der Physik

“…One also can obtain the metal/CdS work function directly from the field at a cathode-adjacent domain {with F II (n c ¼ n II )} and can obtain the work function for different metal contacts [42]. With this method it has, for the first time, been observed that the work function depends to some degree on the optical excitation of the CdS [43].…”

Section: Three States Of Conductivity In Cdsmentioning

confidence: 99%

High‐field domains from dc to 60 GHz

Physica Status Solidi (b)

2011

The history of the high-field domains is given with the description of the experimental and theoretical results of the team of the author in the first decade after their discovery in 1958. This work is done at CdS single crystal platelets that are used as a model substance. The major findings of modern highfield domain research that followed their original research are then reviewed. It is emphasized that all high-field domains are created for reasons of the minimum entropy production principle when the conductivity decreases more than linear within a semiconductor. The application of these high-field domains in important semiconductor devices are reviewed that have now reached a multibillion dollar market.

“…Such a shift by as much as 0.3 eV was observed with changing optical excitation 16. This indicates a substantial change in the dipole layer near the electrode that is responsible for the work function 17.…”

Section: Self‐adjusting Electron Affinitymentioning

confidence: 99%

“…This is difficult to achieve in the laboratory and almost impossible to maintain in the production line of solar cells. All of these facts have been published separately in the past 8, 12–19, but they are here assembled together as they are relevant to thin‐film solar cells (see also relevant review 20).…”

Section: Reasons Why Cds Is Such a Good Layer And Not Other Semiconmentioning

confidence: 99%

Field quenching in photoconductive CdS as possible reason to enhance V_oc and FF in thin‐film solar cells

Physica Status Solidi (a)

2009

Field‐quenching via Frenkel–Poole excitation of Coulomb attractive hole traps limits the field in the CdS part of the junctions to 50 kV/cm. This is far below the field in typical other pn‐junctions of thin‐film semiconductors, which exceeds 100 kV/cm and approaches tunneling fields that make junctions leaky, hence reduces both Voc and FF. Field‐quenched CdS may become electronically inverted, thereby providing a possibility that the junction of the CdS/CdTe cell may extend into the CdS, with the cell becoming a hetero structure. With field quenching a region of negative differential conductivity is created causing a high‐field domain that prevents the maximum electric field in the junction to exceed 50 kV/cm, avoiding tunneling, hence electron leakage through it. A preliminary band model of this cell is proposed.