compare hemt and hbt efficiency

Can anyone give me an idea about the circuit applications for MESFET, HEMT and HBT? For which kind of device is used for what kind of circuits? Are there many companies to do these kind of circuits?

there is a text on this topic: hemts and hbts from artech house.

basically you use hemt, hbt and mesfet with gaas material and no silicon and can also use inp (gaas is gallium arsenide) and inp is inidium phosphide.

you use this when you want very high frequency performance, low noise, high gain, high power, high efficiency and so on (>10GHz usually for these devices).

the hemt and hbt use heterojunctions, which are different than a homojunction found in most silicon chips: a heterojunction uses two disimilar materials back to back which allows different performance and higher perfomance then the same material connected.

many companies make these:

rfmd
triquint
hittite
rayhteon
hughes research labs....many others, mostly military stuff.

check the compound semiconductor symposium at www.csics.org for more information.

seems not a lot of people discuss these devices, so is this easy to find a job for a MS?

depends where you are in the world.

mostly military uses these devices (satellites and other high frequency) - a few companies in the USA i mentioned.

for MS it is hard everywhere to get a job, BUT doing high frequency RF (>10GHz) might make the job search easier.

a very good book

MEMS Reliability Assurance Guidelines
for Space Applications

could be found at

http://parts.jpl.nasa.gov/docs/JPL%20PUB%2099-1.pdf