The Transport Properties Of The Two Dimensional Electron Gas In â…¢-â…¤ Semiconductor Heterostructures

The GaAs or GaN based high electron mobility transistor (HEMT) is one of themost promising high speed semiconductor devices. Due to its properties, such as ultrahigh-speed, low power consumption, low noise, and so on, HEMT is widely used in themicrowave-communication, RF amplifier, signal processing, high-speed computer, etc.The performance of HEMT relies on the transport properties of the two-dimensionalelectron gas (2DEG), i.e., the density and mobility of the two-dimensional electron gas.The mobility, however, is influenced by several different scattering mechanisms, suchas impurity, phonon, defect, and roughness scattering. So, the study of these scatteringmechanisms is significant for the performance optimization the HEMT devices. In thisthesis, we study systematically some of the new scattering mechanisms in the Ⅲ-Ⅴsemiconductor heterostructures under the Boltzmann equation and Born approximation.The results are discussed and interpreted as follows:1. Under the Boltzmann equation, we suggest a new theoretical model to study theanisotropic short-range scattering effect of the elongated type-II quantum dotsembedded in the GaAs/InGaAs double hetero-junction quantum well on thetwo-dimensional electron gas. The results show that the mobility has a maximum valuealong the direction along the direction parallel to the elongtation of the quantum dots，and has a minimum value along the direction along the direction parallel to theelongtation of the quantum dots2. The Coulomb scattering effect of the type-I InGaN quantum dots on thetwo-dimensional electron gas in AlGaN/InGaN/GaN heterostructures is quantitativelyanalyzed. The scattering strength is found to be quickly increase as the dots plane getsclose to the2DEG channel and the dots density increases. Compared with theconventional interface roughness (IR) scattering and alloy scattering, the type-Iquantum dots scattering will be dominant at lower2DEG density and not ignorable athigher2DEG density.3. We develop a new theory to study the anisotropic scattering effect of theinclined misfit dislocation on the two-dimensional electron gas in AlGaN/GaNheterostructures. The results show that the2DEG will be more easily scattered as they move in the direction parallel to the projection of the inclined dislocation line thanperpendicular to the projection, i.e., the electron mobility has a maximum value alongthe direction perpendicular to the projection of the inclined dislocation line, and viceversa.4. We study the effect of surface roughness of the SiN passivation layer on thetransport properties in AlGaN/GaN heterostructures. The surface roughness scatteringstrength of the SiN passivation layer is of the same order as the interface roughness (IR)scattering. Increase the thickness of the SiN passivation layer and the AlGaN layercould increase the the2DEG density, and in turn decrease the surface roughnessscattering strength.5. We study the modulation of the in-plane magnetic field on the two-dimensionalelectron gas transport in AlGaAs/GaAs single quantum well. Due to the the Lorentzforce, the electron wave function will be deformed towards lower or upper interface.Ifthe scatterers are one-side distributed, the in-plane magnetic field will lead to ananisotropic scattering probability, which results in a higher mobility along the directionperpendicular to the magnetic field.