M.Sc Thesis

M.Sc StudentHorn Adi
SubjectDesign and Implementation of Heterostructure Field Effect
Transistor on AlGaN/GaN
DepartmentDepartment of Electrical and Computer Engineering
Supervisors PROFESSOR EMERITUS Gad Bahir


GaN based heterojunction field-effect-transistors (HFET) show great promise for high power microwave applications. The advantages of the GaN material system over the conventional III-V compounds include a larger band-gap, a larger breakdown electric field, a larger conduction band discontinuity between GaN and AlGaN, and the presence of a large polarization field that induces a high two-dimensional electron gas concentration.

In this research we developed a detailed process for AlGaN/GaN HFET, which includes high density of the 2DEG. We present some changes in the material treatments, or in the process itself, to achieve good contacts, which will optimize the HFET behavior at DC and RF. An effort was made to decrease the gate leakage current by using varius surface treatments and the MOS-HFET structure.

We conducted electrical measurements on the devices for DC and RF characteristics. Following the measurements we conducted optimizations to the device.

In order to clarify the origin of one of the main problems in GaN-based HFETs -  current collapse - we studied the temporal behavior of our HFETs under illumination and in the dark. The current measurements were done to develop a physical explanation for the current Persistent Photoconductivity (PPC) instead of the phenomenological stretch exponent model. The explanation is made by using the model of charge capture by surface traps, and by using the measurements of the drift mobility as a function of two dimension electron gas density, which brought us to a better understanding of the 2DEG behavior in the AlGaN/GaN structure in dark and light.