GAINAS/INP AND GAINP/GAAS (100) INTERFACES - AN ULTRAVIOLET PHOTOELECTRON-SPECTROSCOPY STUDY

The formation of GaInAs/InP and GaInP/GaAs (100) lattice-matched heterostructures grown by metalorganic molecular-beam epitaxy (MOMBE) was investigated in situ by ultraviolet photoelectron spectroscopy, using a He discharge lamp. Both direct (Ga0.47In0.53As grown on InP or Ga0.5In0.5P grown on GaAs) and inverse interfaces were investigated, with overlayer thicknesses in the range 1 to 10 monolayers (MLs). The Ga-3d and In-4d core-level (CL) spectra were measured with the He II radiation (hv = 40.8 eV), allowing highly surface sensitive measurements. We first show that the GaInAs and GaInP surfaces immediately after MOMBE growth display In segregation, leading to 100% In composition at both surfaces. A simple model indicates that this In segregation is limited to the first monolayer of ternary material. We have then studied the Ga/In atomic profiles at the various heterostructures studied. Both direct interfaces are abrupt in this respect. The situation is not so simple for the inverse interfaces. In the case of GaAs grown on GaInP, an In layer is detected at the growing GaAs surface, coming from a Ga/In exchange reaction at the first step of the growth of this heterostructure. The equivalent thickness of this InAs-like layer could be measured and is shown to depend crucially on the growth temperature in the range 480-550-degrees-C. For inverse interfaces in the system InP/GaInAs, we sometimes observe Ga diffusion in the InP layer, but this is not systematic, and the driving growth parameter for this phenomenon could not be identified. Taking into account these chemical configurations of the interfaces, we have undertaken a determination of the valence band offsets (VBOs) from the shifts of CL spectra. For GaInAs/InP, interfaces, we find a value of 440 +/- 50 meV for the direct case, in very good agreement with both experimental and calculated values, whereas for the inverse case we obtain a VBO of 260 +/- 50 meV. This strong asymmetry is discussed in parallel with the chemical asymmetry observed previously, in particular the fact that the inverse interfaces involve the growth of an InP layer on an In-segregated GaInAs surface. For GaInP/GaAs interfaces, we obtain values for the VBO very close to zero for both heterostructures. This behavior is discussed in connection with the observation that interfaces in this system are not well-known and published values for the VBO cover almost the entire band gap difference.