【摘要】 研究发现,氮化镓外延单晶中束缚于中性施主中心和受主中心上的束缚激子BED°和BEA°的复合发光,具有偏振特性。这种偏振特性,会随激发光的强度发生变化。当激发光的强度在10~4W/cm~2和10~6W/cm~2间变化时,偏振度首先以二次方的规律随激发光强的增强而增加,而后超于饱和。本文首先用单轴晶体中介电函数的各向异性解释了荧光固有偏振度的起因,继而采用束缚激子间相互作用的电偶极子模型解释了荧光偏振度随激发光光强的变化规律。更多还原

【Abstract】 The polarization properties of the three kinds of bound excitons bounded at neutral donors(BED0) neutral acceptors(BEA0) and Donor-Acceptor pairs (D-A) in GaN crystals were studied. The polarizability of the emission of BED0 and BEA0 increases quaduatically with the increase of the excitation intensity (Iex) in the range of 104W/cm2-106W/cm2. And a saturation appears thereafter. The initial polarization of the photoluminescence from BED0 and BEA0 can be explained by the anisotropic dielectric constant of uniaxial crystal. And the change of polarization with the Iex is due to the different extent of the dipole-dipole interaction between bound excitons at different density.The GaN crystal layers were grown by the VPE on sapphire substrates oriented in the (0001) direction. The samples were put in the crystal ESR-900 and cooled down to 77K. And they were then excited by a light beam of wavelength of 308nm from an excimer laser EMG-102.With a set if neutral attenuators and a lens, Iex on samples could be easily changed from 104W/cm2 to 107W/cm2. A polarizer was put before a double grating monochrometer to pick out bound exciton emissions polarized in parallel and vertical directions to the C-axis of GaN wafers respectively.After the monochrometer, the light signal was messured by a photomultiplier C-31034 with cooling system and recorded by a X-Y recorder.Fig.1 and Fig.2 show the emission spectra of different samples. Fig.3 shows the optical scattering plane in experimental setup. Fig.4 and Fig.5 show the P values under different Iex for different samples.Therelations of BED0 and BEA0 are shown in Fig.6 and Fig.7 respectively.From Fig.6 and Fig.7,we can see that the ralationP= (A+BIex)2 (7)is valid in the Iex range of 103W/cm2-105W/cm2. When Iex is higher than 105W/cm2, P tends to a saturation point. It might be caused by the concentration limitation of neutral donors and neutral acceptors.更多还原