DISLOCATIONS, TWINS, AND CRACKS IN IN1-XGAXP (001)GAAS HETEROEPITAXIAL LAYERS/

The occurrence of dislocations, twins, and cracks in In1-xGaxP (0.42 l ess-than-or-equal-to x less-than-or-equal-to 0.75), i.e. layers grown under compression and tension on (001) GaAs substrates of different mi sorientation (0-degree, 2-degrees, 6-degrees) towards [010], is studie d for layers of various thicknesses (1 to 2.7 mum). On the surface of layers grown under tension corrugations due to preferred slip on (111) and (1BAR1BAR1) of the [11BAR0] zone can be observed. Additionally, f racture occurs at higher misfit strain, but in [110] direction, i.e. t he cleavage plane is (11BAR0). The well-defined surface corrugations p arallel to [11BAR0] correlate to twin lamellae located on inclined {11 1} slip planes. Twin growth proceeds by nucleation and propagation of 90-degrees Shockley partial dislocations from a surface-near region to wards the layer-substrate interface, leaving a less mobile 30-degrees partial behind (in the case of tension). It seems that Maree's concept ion of spontaneous half loop nucleation at the free surface of a growi ng layer with critical thickness is favoured. In layers grown under co mpression the same model is used to explain the formation of dislocati on networks. In this case the front segment of half loops generated at the free layer surface consists of a leading 30-degrees Shockley part ial and the 90-degrees one trailing behind. Because of the lower mobil ity (higher friction force) of the first one, the twin formation is su ppressed. From simple crystallographic arguments (InGaP belongs to the space group F 4BAR3m) it is concluded that in layers grown under tens ion partial dislocations with excess In/Ga atoms in their core can eit her be generated or be moved more easily than dislocations with excess P atoms. In layers grown under compression, on the contrary, partials with excess phosphorus in their core can be either generated or be mo ved more easily than partials with excess In/Ga atoms. Using the model of spontaneous half loop nucleation at the growing surface the demarc ation line between the dislocation- and twin-free growth and that wher e defects occur is calculated and determined experimentally for deposi tion temperatures between 525 to 750-degrees-C. Moreover, the fracture toughness and precursor crack length for layers grown under tensional stress conditions are estimated using a modified Griffith equation an d are K(IC) = 0.696 MPa m1/2 and l(c) = 216 nm (at 720-degrees-C). Twi n formation begins at 720-degrees-C if a critical strain of epsilon(c) = 3.1 x 10(-3) and, therefore, a critical shear stress of tau(c) = 87 .5 MPa is exceeded.