MBE Growth Of InP Based PHEMT Epitaxial Materials

InP is an excellent III-V compound semiconductor material and is widely used as the material for the microwave and millimeter-wave devices. HEMT is a kind of high speed semiconductor device that bases on the heterojunction modulation doping. InP PHEMTs have demonstrated excellent high-frequency and low-noise performance, but the power performance needs to be improved further. Two-dimensional electron gas density and electron mobility are two important factors which affect the power performance of InP PHEMT devices. Therefore it is very necessary to study the main factors which affect two-dimensional electron gas density and electron mobility for fabricating InP PHEMT epitaxial materials with high μ_n×n_s.In this thesis, the effects of single side doping structure and double sides doping structure, spacer layer thickness, channel's In composition, various quantum well structures on two-dimensional electron gas density and electron mobility have been studied. The samples of InP PHEMT epitaxial materials have been fabricated by MBE technique, then have been tested by AFM, Hall, electrochemistry C-V, X-ray double crystal diffraction and photoluminescence system.In conclusion, we obtained some results from a lot of experiments, and the main results are as follows:1 , At 300K and 77K, two-dimensional electron gas densities of the double sides doping sample are 50% higher than those of the single side doping sample, but electron mobilities of the single side doping sample are respectively 12%, 29% higher than those of the double sides doping sample. This shows that double sides doping structure can increase two-dimensional electron gas density, but it simultaneously increases the ionization impurity scattering and the interface roughness scattering, so double sides doping structure decreases electron mobility.2, The effects of spacer layer thickness on two-dimensional electron gas density and electron mobility are different. The thicker spacer layer thickness is, the less free electrons transfer to channel. The increase of spacer layer thickness can decrease two-dimensional electron gas density, however, it simultaneously reduces the ionization impurity scattering, so it increases electron mobility. We found out that when the top and the bottom spacer layer thickness are respectively 55A and 50A, μ_n×n_s are best.3, The increase of channel's In composition can increase two-dimensional electron gas density and electron mobility to some extent. But, if channel's In composition is too high, it will deteriorate epitaxial quality, and decreases two-dimensional electron gas density and electron mobility For the single side doping samples and the double sides doping samples, when channel's In composition is 65%, μ_n×n_s are best.4, At 300K and 77K, the square-well sample has best μ_n×n_s among various quantum-well structures samples. Two-dimensional electron gas densities of the V-shape-well sample and the double-squares-well sample are higher than that of the square-well sample, but electron mobility of the V-shape-well sample and the double-squares-well sample are all smaller than that of the square-well sample, so μ_n×n_s of the V-shape-well sample and the double-squares-well sample are not so good as that of the square-well sample.Basing on the above researches, the single side doping structure and double sides doping structure InP PHEMT epitaxial materials with high μ_n×n_s have been fabricated by MBE technique. At 300K and 77K, the single side doping sample's μ_n×n_s are respectively 3.43× 10¹⁶/V .s, 13.66×10¹⁶/V .s, and the double sides doping sample's μ_n×n_s are respectively 4.81 ×10¹⁶/V .s, 14.93×10¹⁶/V .s. These parameters are in the advanced level in our country.