Reverse bias: J-V characteristics

Forward bias J-V characteristics

Organic Semiconductor

An organic semiconductor is an organic material with semiconductor properties. That is, with an electricalconductivity between that of insulators and that of metals. Single molecules, short chain (oligomers) and organicpolymers can be semiconductive. Semiconducting small molecules (aromatic hydrocarbons) include the polycyclic aromatic compounds pentacene, anthracene, and rubrene. Polymeric organic semiconductors include poly(3-hexylthiophene), poly(p-phenylene vinylene), as well as polyacetylene and its derivatives.

Typical current carriers in organic semiconductors are holes and electrons in π-bonds. Almost all organic solids are insulators. But when their constituent molecules have π-conjugate systems, electrons can move via π-electron cloud overlaps, especially by hopping, tunnelling and related mechanisms. Polycyclicaromatic hydrocarbons and phthalocyanine salt crystals are examples of this type of organic semiconductor.

Mainly due to low mobility, even unpaired electrons may be stable in charge-transfer complexes. Such unpaired electrons can function as current carriers. This type of semiconductor is also obtained by pairing an electron donor molecule with an electron acceptor molecule.

Notes from wikipedia:  http://en.wikipedia.org/wiki/Organic_semiconductor#Characterization

Band Diagram for n type Schottky Diode

Notes from http://www.tmi.vu.lt/legacy/pfk/funkc_dariniai/diod/schottky.htm

Schottky Diode VS P-N Diode

Schottky Diode

Reverse current due to majority carriers that overcome the barrier.
less temperature dependence

Forward current due to majority injection from the semiconductor.

The cut-in voltage is quite small.

Switching speed controlled by thermalization of hot injected electrons across the barrier. few picoseconds.

Essentially no recombination in depletion region.
ideality factor 1.0

P-N Diode

Reverse current due to minority carriers diffusing to the depletion layer.

strong temperature dependence

Forward current due to minority carrier injection from n- and p- sides.

Forward current needed to make the device conducting (the cut-in voltage) is large.

Switching speed controlled by recombination (elimination) of minority injected carriers.

ideality factor in I-V charateristics 1.2-2.0 due to recombination in depletion region.

Reference: 
 Semiconductor devices : an introduction / Jasprit Singh. 

WEEK 1-2

After the first meet with the supervisor, we were going to search for the related information on the project specifically. In the first week, we need to find and master the concepts of metal-semiconductor diodes. As the results, it was necessary to know the basic characteristic of metal-semiconductor contacts.

Refer to Semiconductor Devices (2^nd edition), written by S.M.Sze, we get the information that the metal practical semiconductor contacts was the first practical semiconductor device in the form of a point contact rectifier. A metallic whisker pressed against a semiconductor.

The characteristics of point contact rectifiers were not reproducible from one device to another, which have been largely replaced by metal-semiconductor contacts fabricated by planar processes.

The following figures are the results of the information about metal semiconductor devices for log book.

Figure 1

Figure 2

Figure 3

Figure 4

Written in 24th Feb, 2013

Brief explanation for this project

A mini-project is required to be implemented in Semester 2 Year 2. The project called ‘Modeling electrical properties of Organic Schottky diodes’ was distributed to my group. Before the project beginning, our two members group had contacted the supervisor of this project and met with her to prepare with it.

The project began when this semester started. Due to some reasons, it did not start until week 2 in semester 2. This blog will give the processes of carrying out the project step by step and renew when we have the latest process.

Here is the basic information for this project

Research group No.: 91

Participants: Tong, Zhang & Yiwei, Zheng

Department: Electrical and Electronic Engineering

Supervisor: Dr. Raja

Project name:

Modeling electrical properties of Organic Schottky diodes

Required experimental materials and equipment:

PC, MATLAB software

Project started date: 6^th Feb, 2013

Expected finished date: 8^th Mar, 2013