Effect Of Depolarization On The Optical Susceptibilities In The Laser Dressed Modulation Doped Alxga1xn Gan Single Quantum Well

Abstract

newline The III-nitride semiconductors are significantly favourable materials for electronic and optoelectronic applications. Being direct wide band gap semiconductors III-nitride are the excellent choice for LED and other optoelectronic devices to cover spectral range. Furthermore, red, blue and green colours can be combined to produce white LEDs for long lasting and efficient illumination. Other applications include sensors, indicator lamp for instrumentation and automobile instrument panel illumination. GaN-based UV photo detectors are increasingly being used for defence and space applications like missile plume detection systems, solar UV monitoring and detection, flame sensors, UV source calibration and secure space communication. All the above properties can be speculated by studying the nonlinear optical properties in the hexagonal quantum well. newlineThe hexagonal quantum well (QW) fabricated using heterostructures of wurtzite semiconductors AlGaN and GaN is attractive for nonlinear optical studies in the near-infrared range due to large intersubband energy spacing. Compared to cubic QW, the barrier height in the hexagonal QW is higher as the band gap difference between AlGaN and GaN is high. The conduction band offset is also higher in hexagonal quantum well. The higher barrier height increases the intersubband energy separation. newlineThe single quantum well based AlxGa1-xN/GaN hexagonal nitride semiconductors heterostructure has an internal electric field inside the well region due to spontaneous and piezoelectric polarizations. The sp3-hybridized orbitals in the hexagonal semiconductors with wurzite structure are tetrahedrally bonded as in cubic zincblende structure. The atoms in the zincblende structure are placed in symmetrical configurations. On the other hand, the atoms are not placed symmetrically beyond second neighbours in wurtzite structure. As a result of this more charge is cantered on the [0001] direction by pushing charge slightly out of the other three bonds. The asymmetry in the charge distribution produces electrostatic spontaneous polarization. The spontaneous polarization vanishes in the cubic QW. The piezoelectric polarization arises from the lattice mismatch in the wurtzite structure. Both the polarizations yield an internal built-in electric field inside the well region of the QW. In cubic QW, the second-order optical susceptibilities can t not be obtained due to the off-diagonal dipole matrix elements are vanished, while in wurtzite QW all the orders- of optical susceptibilities can be determined. Hence group III nitride wurtzite QWs are good choice for studying the nonlinear optical properties in different optoelectronic devices.