After the first meeting with our supervisor, we are required to do more reading in order to have a deeper understanding of our project. The below text is some basic notes about organic schottky diodes.
The above symbol is the schottky diode; it is defined as a semiconductor diode with a low forward voltage drop and a very fast switching action which are caused by Schottky barrier. The anode is metal and cathode is semiconductor (p-type). Here are the forward bias I-V characteristics of a pn junction diode and schottky barrier diode.
The current in a pn junction diode is controlled by the diffusion of minority carriers. The current in a Schottky diode results from the flow of majority carriers over the potential barrier at the metallurgical junction. This means that there is no minority carrier storage in the Schottky diode, so the switching time from a forward bias to a reverse bias is very short compared to that of a pn junction diode. The storage time, ts, for a Schottky diode is essentially zero. In addition, the reverse-saturation current Is for a Schottky diode is larger than that of a pn junction diode for comparable device areas. This property means that it takes less forward bias voltage to induce a particular current compared to a pn junction diode. We can also determine that the Schottky diode has a smaller turn-on voltage than the pn junction diode.
Moreover, we also find some basic information about organic semiconductor. We know that an organic semiconductor is an organic material semiconductor properties. There are mainly two differences between organic and inorganic semiconductor. The first is the different shapes of crystals. In terms of organic semiconductor, it is Van der Waals bonded crystal while inorganic is covalently bonded crystals. In addition, their materials are also different. Organic semiconductor is polymer based organic material while inorganic one is silicon based inorganic material.
When talking about advantages and applications. The organic semiconductor is cheaper, lighter and more flexible than inorganic semiconductor. But it may have high resistance and shorter lifetimes. Finally, organic semiconductor could be used in the display system, like organic light emitting diodes (OLED), it can also be used as RFID (Organic Nano-Radio Frequency Identification Devices) and solar cells.
In addition, we borrow a book named <<Metal-Semiconductor Schottky Barrier Junctions and Their Applications>> which edited by B.L. Sharma, With the help of this book, we had a better understand about energy band diagram and metal-semiconductor contact.
Firstly, we searched some information about potential barrier: We know that it is formed when a metal is contacted with a semiconductor and arised from the separation of charges at the metal-semiconductor interface. Secondly, we explored the energy band diagram about p-type.
when before contact, there is no charges at the surface so that there is no band bending.
When the semiconductor and metal contact, the valance band and conduction band were bent as shown below. In this case, there is no current flowing in the metal-semiconductor contact, and the built-in potential Vi is formed.
On forward bias, the energy level diagram is shown below.
The final figure is how the energy changes on reverse bias.
Reference:
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