I have a basic question regarding silicon-based MOSFETs and alternative MOSFETs such as InGaAs.
I am aware of the fundamental equations in which describe the current flow for the silicon channel MOSFET but I'm curious to know if the equations hold for InGaAs. I understand that the basic parameters will change, such as the electron mobility and the gate oxide capacitance (assuming different interfaces are used). But do the fundamental equations hold? For example, what about the equation below?
$$ I_d = \dfrac{1}{2}k'_n \dfrac{W}{L}V_{OV}^2$$
For example, if someone gave me a diagram of an InGaAs MOSFET, and told me to calculate the current through the device considering all three regions of operation (saturation, triode, subthreshold) and for both long and short channel, could I still open up any analog CMOS book, grab the equations I need and calculate which is needed?
From all the papers I've read so far, the equations seem to hold regardless of the material.
Best Answer
What you're talking about is an electrical model of a transistor, not necessarily a fundamental equation of how semiconductors work. As far as models go, it's a fairly simple one, not taking into account many behaviors and parameters. Typical models for computer-based simulation, such as BSIM3/BSIM4, have hundreds of parameters to more accurately model what the transistor is doing under more conditions.
Your example equation -
$$ I_d = \dfrac{1}{2}k'_n \dfrac{W}{L}V_{OV}^2$$
is a simple model useful for evaluating analog designs. Its use is in understanding relationships and dependencies for various parameters, such as bias currents and transistor sizing.
There will be some behavior that your device will have that is poorly modeled by these equations. Something as simple as non-constant output resistance in saturation might be an example, or maybe it does something really funky. There may be odd temperature dependencies that are unexpected.
When doing some "not silicon" analog design, I've seen that these simple models are sometimes inadequate. The basic premises that they have are still useful.