Factors influencing the varaiation of depletion capacitance of MOS capacitor

[KITTU123]

Hi , i am interested to know physics behind MOS capacitors, on which iam currently working in . i started to fabriacate a MOS capacitor without using oxide (silicon dioxide) layer, i have read in articles that a MOS capacitor can be fabricated by using the native oxide layer ( naturally formed ) as an insulator in between the metal contact and semiconductor.i observe a relevant results (similar to MOS capacitor). but i observe that there is no stable characteristics in cv measurents from one sample to other sample.i.e especially near the depletion mode of operation the curve are approaching both towards negative direction of voltage of certain sample and the curves of other sample are approaching in positive direction of voltage.which is undesirable. can i know the reasons affecting the instability in these characteristics and methods to get a stable behaviour. please suggest me the topics along with a good book to be read , in order to understand the physics behind this.

 

[hasib_eee]

Hello. You have to go through the detail of a PN junction first. Then a P+n junction. A MOS capacitor in depletion mode is almost like a P+n or N+p junction. P+ or N+ means that part is heavily doped.

MOS capacitor CV curve depends on many parameters, like oxide thickness,substrate doping, fixed oxide charge,interface trap charge, frequency of CV measurement.

S.M.SZE's book about device physics has a wonderful chapter about MIS capacitor. You can refer to that for better understanding.

Best Regards.

M.Satter.

 

[ravenprp]

There are several factors that can influence the variation of depletion capacitance in a MOS capacitor. These include the type of semiconductor material used, the thickness and quality of the oxide layer, the doping concentration of the semiconductor, and the applied voltage.

In your case, the lack of a uniform oxide layer may be the main cause of the instability in your measurements. The native oxide layer can vary in thickness and quality, leading to variations in the capacitance values of different samples. This can also affect the behavior of the depletion region, leading to differences in the voltage at which the depletion mode occurs.

Other factors that can contribute to instability in MOS capacitors include surface defects on the semiconductor surface, impurities in the oxide layer, and variations in the metal contacts. These can all affect the electrical properties of the capacitor and lead to inconsistent measurements.

To better understand the physics behind MOS capacitors, I would recommend reading books on semiconductor physics and device fabrication, such as "Semiconductor Devices: Physics and Technology" by Sze and "Fundamentals of Semiconductor Fabrication" by May. These books cover the principles and processes involved in creating MOS capacitors and can help you understand the factors that can affect their behavior.

In order to achieve a more stable behavior in your measurements, it may be helpful to improve the uniformity of the oxide layer and ensure consistency in the fabrication process. Additionally, using higher quality materials and carefully controlling the doping concentration can also help reduce variations in the depletion capacitance.