{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Chapter 6 Lecture - Part 1

In this example the device is isolated from others on

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: esn’t To increase with V above VP increase GaAs MESFET formed on an n-type GaAs layer grown epitaxially on a semi-insulating substrate. In this example the device is isolated from others on the same chip by etching through the n region to the semi-insulating substrate. MESFET MESFET • Definition: Definition: – • Basically it’s a JFET that uses a reversed biased Basically Schottky contact instead of a p-n junction to regulate current flow in the channel. regulate Main uses: Main – High speed digital and microwave devices that High require very tight geometric tolerances. Schottky contacts have very sharp interfaces with semiconductors, unlike some p-n junctions semiconductors, MESFET MESFET • Example: GaAs MESFET (Figure 6.7) – Description: • Substrate: semi-insulating GaAs • Semiconducting layer: n-type GaAs epitaxial thin film – Why GaAs • Higher electron mobility than Si • Allows for tight geometric tolerances by way of epi Allows growth or ion implantation growth • Channel length L of 0.25 microns possible. HEMT HEMT • High Electron Mobility Transistor – Definition: a device that uses heterojunctions to Definition: increase the conductivity of the channel without using doping to do so. doping – Why important: increasing conductivity via doping Why tends to decrease the mobility due to impurity scattering tends • Structure – A thin undoped well is bounded by doped barriers of a thin higher bandgap (AlGaAs-GaAs-AlGaAs) higher – This leads to a potential well • Effect HEMT HEMT – Electrons in the doped boundary regions diffuse into Electrons the GaAs and become trapped in the well the – The effect is to separate the donors from their The electrons physically electrons – The net effect is to get numerous electrons in an The otherwise undoped (or lightly doped) region otherwise – Conductivity is enhances but mobility is not lowered. • Important characterstics – Large electron density (1012/cm2) – Very thin undoped layer (...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online