The electronic properties of a surface of a material are different from its volume properties. It is required to underline the surface properties and their effect on the performance of the materials and consequently on the devices such as bipolar devices and mos devices.
The defect density on the surface plays a crucial role for bipolar transistor or MOS structure. These devices are usually prepared in cleanroom (1-100) to avoid surface contamination. Typical passivation is achieved by thermal silicon dioxide on the surface of silicon wafers. Another important section is the wafer cleaning from dust and organic components by IPA, hydrofloric acid and acetone. With larger and thinner silicon wafer the surface passivation will play a crucial role in CMOS and transistor.
Solar cells on the other end are processed in semiclean room (1000-10000). Modern surface passivation in c-Si solar cells can reduce surface loss to less than 0.5%.
Surface plays an important role for optoelectronic devices. For example, in case of solar cell: the proper surface passivation enhances the efficiency by reducing the surface recombination.
The defect density on the surface plays a crucial role for bipolar transistor or MOS structure. These devices are usually prepared in cleanroom (1-100) to avoid surface contamination. Typical passivation is achieved by thermal silicon dioxide on the surface of silicon wafers. Another important section is the wafer cleaning from dust and organic components by IPA, hydrofloric acid and acetone. With larger and thinner silicon wafer the surface passivation will play a crucial role in CMOS and transistor.
Solar cells on the other end are processed in semiclean room (1000-10000). Modern surface passivation in c-Si solar cells can reduce surface loss to less than 0.5%.
Surface defects can lead to early breakdown of power devices. Therefore, surface passivation plays very important role for device reliability.
Interface defect density (Dit) is a very critical parameter to control In MOS or MIS based devices. Surface defects lead to interface defect states and interface charges, therefore, it is important to have good interface of dielectric with semiconductor. In addition, these defects affect surface recombination velocities (SRV).
At first i would like to thank all colleagues who contributed to the answer of my question about the effect of surface on the material and device performance. Here i will try to sum up all answers and add some aspects which may be of importance for the electronic Marerials and devices engineers.
Surfaces are the planes surrounding the volume of the material. Here we assume that the martial is in form of crystal. Therefore the surface terminates the periodicity of the crystal . Accordingly, the surface will be geometrically distorted and may be chemically active reacting with oxygen..Here we assume ideal surface which is not chemically contaminated. Such surface has the following effects on the electronic properties of electronic material:
- It forms a potential barrier at the surface preventing the conduction electrons from leaving the interior of the material. It confines the electrons inside the material. To take it into account, one defined the work function of the material which is a material property.
-Because of the interruption of the periodicity of the material, localized electronic states are formed in the energy gap at the surface of the material.These localized states acts as traps and recombination centers for mobile charge carriers.These surface defects will also increase the scattering of the mobile charge carriers in the surface region. Consequently:
- The recombination rate of minority carriers increases at the surface and it is accounted for by the surface recombination velocity vs.
- The additional scattering of the mobile charge carriers at the surface and their reflection at the surface decreases the mobility of the charge carriers. This is accounted for by the socalled surface mobility mus in addition to the volume mobility
-Surface state can trap charge carriers for relatively long time leading to formation of charged surface layer.
These are the main effects of the surface on the material properties and how are these effects are described. These effects can be mitigated by:
-Increasing the volume to surface area.
-Passivating the surface with oxydation or hydrogenation or any other suitable.substances.
The effect of surfaces on devices is easily determined from their effects on the material as the device characteristics are directly related to the material properties.
Moreover, the colleagues pointed out these effects on the devices performance.
Surfaces generally have bad effects on the device performance except for ohmic contacts.
Thank you
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