Effect of Te doping on step structure and ordering in GaInP

Abstract

The effects of Te doping on the step structure and CuPt ordering in GaInP grown on vicinal (0 0 1) substrates have been investigated. The free electron concentration was found to be proportional to the diethyltelluride (DETe) flow rate. No saturation effects were found to concentrations as high as 8.4×10 18 cm −3. Te is a very efficient dopant with a distribution coefficient of k Te=10 for the vicinal layers (misoriented by 3° in the (1 1 1)B direction) at a growth temperature of 670°C. The Te distribution coefficient had a slightly higher value of 19 for singular (0 0 1) 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 by 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 markedly over the range of doping that produced disordering. Step bunching occurred at 670°C in the undoped layers, but disappeared completely at electron concentrations of ⩾6×10 17 cm −3. Thus, Te doping significantly improves the surface morphology viewed using atomic 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 ̄ 1 0] steps due to kinetic effects at the step edges. Bunching apparently disappears due to the increased sticking coefficients of group III adatoms at “up” steps, although thermodynamic explanation cannot be ruled out.