Study On The Structure And Electric Behavior Of GaAs/AlGaAs HEMT

Molecular Beam Epitaxy (MBE) method has been used to grow GaAs/AlxGa1-xAs High Electron Mobility Transistor (HEMT) epitaxial layer on GaAs (001) substrate in this paper. The mobility (μ) can reach to 7950cm2/V·s at 300K and 140000cm2/V·s at 77K, the sheet carrier concentration (ns) is 6.25×1011cm-2 at 300K and 5.78×1011cm-2 at 77K, It comes up to internal advanced level.By employing Daniel Delagebeaudeuf and Nuyen T.Linh's theoretical models, we calculate the changes of ns with doped level (ND), thickness of spacer (di) and aluminum content (x) in AlxGa1-xAs. Then we get the structure of HEMT. To optimize the MBE growth condition of HEMT we grow many specimens with different structure. Si doped epitaxial films are used to research the doped characteristic; GaAs/AlxGa1-xAs heterostructure spicemen are used to control x in AlxGa1-xAs; Superlattice specimen is used to control the thickness of spacer. Then we get high quality HEMT specimen based on the sturcture design and the optimizing of grown condition at last.The crystal quality of specimens have been investigated by means of double crystals X-ray diffraction (DXRD); atomic force microscope (AFM) is used to research the surface appearance; the characteristic of Si doped specimen is investigated by electrochemistrical capacity voltage (ECV) and the Electric behavior is researched by Hall effect measurement.It is showed in the experiments that the substrate temperature makes great effect on the material properties: The surfaces of heterostructure and HEMT specimen prepared under 640℃are smoother and the surface roughnesses are lower. The ns andμof the HEMT specimen increased with the increasing of the substrate temperature.Operation temperature and thickness of spacer both have great effect on the electrical properties of HEMT. Theμof the HEMT specimen increased and the ns decreased with the increasing of operation temperature. The mobility and ns are increased more remarkably when the operation temperature is 77K than 300K. Theμof the HEMT specimen increased with the increasing thickness of spacer, but the ns decreased with it.At last, the effect of rapid thermal annealing on the electrical properties of HEMT material is studied. It was showed that theμdecreased with the increasing of the annealing temperature. And the ns increased in a certain annealing temperature range.