Effect of Te doping on step structure and ordering in GaInP

The effects of Te doping on the step structure and CuPt ordering in GaInP g rown on vicinal (001) substrates have been investigated. The free electron concentration was found to be proportional to the diethyltelluride (DETe) f low rate. No saturation effects were found to concentrations as high as 8.4 x 10(18) cm(-3). Te is a very efficient dopant with a distribution coeffic ient of k(Te) = 10 for the vicinal layers (misoriented by 3 degrees in the (111)B direction) at a growth temperature of 670 degrees C. The Te distribu tion coefficient had a slightly higher value of 19 for singular (001)layers . The degree of order was observed to decrease dramatically with increasing Te concentration, with a value of approximately 0.5 for undoped epitaxial layers and zero for high Te doping levels. The bandgap energy was changed b y 110 meV as the Te doping level was increased from 10(17) to 10(18) cm(-3) . The step structure, observed using atomic force microscopy, changed marke dly over the range of doping that produced disordering. Step bunching occur red at 670 degrees C in the undoped layers, but disappeared completely at e lectron concentrations of greater than or equal to 6 x 10(17) cm(-3). Thus, Te doping significantly improves the surface morphology viewed using atomi c force microscopy. The degree of order and surface structure were observed to change at exactly the same doping concentration. This suggests that the disordering may be controlled by the fast propagation of [(1) over bar 10] steps due to kinetic effects at the step edges. Bunching apparently disapp ears due to the increased sticking coefficients of group III adatoms at "up " steps, although thermodynamic explanation cannot be ruled out. (C) 1998 E lsevier Science B.V. All rights reserved.