Step structure and ordering in Zn-doped GaInP

Abstract

GaInP grown on (001) substrates by organometallic vapor phase epitaxy is typically highly ordered. The driving force is due to the [1̄10] oriented P dimers on the surface. There are apparently additional kinetic factors related to surface steps that also play a key role in the ordering mechanism. However, the mechanism remains undetermined. This work presents the effects of Zn on the step structure and ordering during epitaxial growth. The degree of order is estimated from the low temperature photoluminescence peak energy to be approximately 0.5 for undoped epitaxial layers and the layers are completely disordered at Zn doping concentrations [from dimethyzinc (DMZn) addition to the system] of >1.7×1018 cm−3. This is verified by transmission electron diffraction results. As a consequence, the band gap energy increases by 110 meV as the Zn doping level is increased from 3×1017 to 1.7×1018 cm−3. The [1̄10] and [110]-step spacing as well as the root-mean-square roughness are found to be unchanged over the range of doping that produces disordering for both singular (001) and vicinal substrates. This indicates the disordering mechanism induced by Zn does not involve the step edge adatom attachment kinetics as previously reported for Te. The disordering is believed to be caused by the intermixing of Ga and In due to the increase in diffusion coefficient caused by the introduction of Zn. Modulation of the DMZn flow rate during growth has been used to grow heterostructures and quantum wells. No well boundaries were observed by transmission electron microscopy for thin wells, although both ordered and disordered regions are observed in 50 nm “wells.” This is believed to result from Zn diffusion between the layers during growth.