|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||JJ3, Anisotropic Carrier Mobility in GaN Quantum Well Grown in Non-Polar Direction: Polarization Induced Dipole and Interface Roughness Scattering
||Aniruddha Konar, Tian Fang, Nan Sun, Debdeep Jena
|On-Site Speaker (Planned)
GaN-heterojunction based high-electrom mobility transistors (HEMT) has paved the way towards high speed, high power electronics. Though the built-in polarization field in polar-GaN (grown along c axis) has been exploited to achieve dopant free HEMT, for optical devices polarization field plays a negative role due to quantum confined Stark effect. GaN grown in polar direction cannot be used in bipolar devices due to unavailability of hole doping. Moreover, polar GaN-based MOSFET is hard to pinch-off due to inherent presence of two dimensional electron gas (2DEG) at GaN surface. So the recent trend is to explore optical and transport properties of GaN grown in non-polar (m or a plane) direction. Though optical properties of non-polar GaN based devices have been studied quite extensively, transport properties of these devices have not been addressed so far. In this work, we have theoretically investigated charge transport in non-polar GaN quantum well (QW) structures.
Let us consider a thin non-polar GaN QW of thickness a sandwiched between aluminum nitride (AlN) barrier as shown in fig. 1a). To consider charge transport in this structure, we have figure out all sources of disorders present in the QW. One of the most important source of scattering mechanism for thin QW is interface roughness (IRF) as a result of improper growth conditions. GaN, grown along non-polar direction (m plane) shows parallel trench/stripe like patterns which extend infinitely perpendicular to c axis in the plane of GaN. Another new source of disorder in our structure is the polarization bound charges associated with each interface roughness. The difference of in-plane polarization of GaN and AlN induces bound charges at opposite faces of each roughness as shown in fig.1b). These bound charges can be modeled as infinite line charges ( fig 1c)) and carrier can scatter from the potential originating from these line charges. We have also considered remote ionized impurity scattering and polar optical phonon scattering in our calculation.
Among all the scattering mechanisms mentioned in the above section, interface roughness and polarization-induced line charge scattering are anisotropic (carrier does not feel any potential along the direction of roughness and line charges) but remote ionized impurity and polar-optical phonon scattering found to be isotropic in nature. Using Fermi golden rule and Boltzmann transport equation electron mobility has been calculated. Mobility also shows anisotropic behavior as shown in fig. 2. At room temperatures mobility anisotropy washes out due to strong isotropic polar-optical phonon scattering.
In conclusion, we have investigated the charge transport in GaN QW grown in non-polar direction and predicted anisotropic nature of carrier mobility.