Kuilong Li

Characterizations of high-voltage vertically-stacked GaAs laser power converter

Six-junction vertically-stacked GaAs laser power converters (LPCs) with n+-GaAs/p+-Al0.37Ga0.63As tunnel junctions have been designed and grown by metal-organic chemical vapor deposition for converting the power of 808 nm lasers. The LPC chips are characterized by measuring current–voltage (I–V) characteristics under 808 nm laser illumination, and a maximum conversion efficiency ηc of 53.1% is obtained for LPCs with an aperture diameter of 2 mm at an input laser power of 0.5 W. In addition, the characteristics of the LPCs are analyzed by a standard equivalent-circuit model, and the reverse saturation current, ideality factor, series resistance and shunt resistance are extracted by fitting of the I–V curves.

Control of symmetric properties of metamorphic In0.27Ga0.73As layers by substrate misorientation

Asymmetry in dislocation density and strain relaxation has a significant impact on device performance since it leads to anisotropic electron transport in metamorphic materials. So it is preferred to obtain metamorphic materials with symmetric properties. In this paper, we grew metamorphic In0.27Ga0.73As epilayers with symmetric low threading dislocation density and symmetric strain relaxation in two 〈110〉 directions using InAlGaAs buffer layers on 7° misoriented GaAs (001) substrates. To understand the control mechanism of symmetric properties of In0.27Ga0.73As layers by the substrate miscut angles, In0.27Ga0.73As grown on 2° and 15° misoriented substrates were also characterized as reference by atomic force microscopy, transmission electron microscopy, and high resolution triple axis x-ray diffraction. The phase separation and interaction of 60° misfit dislocations were found to be the reasons for asymmetry properties of In0.27Ga0.73As grown on 2° and 15° substrates, respectively. Photoluminescence results proved that the In0.27Ga0.73As with symmetric properties has better optical properties than the In0.27Ga0.73As with asymmetric properties at room temperature. These results imply that high quality metamorphic In0.27Ga0.73As can be achieved with controllable isotropic electron transport property.

Effects of Substrate Miscut on the Quality of In0.3Ga0.7As Layers Grown on Metamorphic (Al)GaInP Buffers by Metal–Organic Chemical Vapor Deposition

In0.3Ga0.7As layers were grown by metal–organic chemical vapor deposition utilizing compositionally step-graded (Al)GaInP buffers on different misorientated GaAs substrates. The substrate miscut toward the [110] direction promotes α dislocation glide along the [110] direction while it exerts an adverse effect on β dislocations in the perpendicular direction with increasing the miscut degree. In comparison with the 2° and 7° samples, a better surface morphology with a RMS roughness of 5.77 nm and a lower density of threading dislocations indicated by the photoluminescence and transmission electron microscopy results were obtained in the 15° sample.