Showing papers by "Jean Massies published in 1996"

Nitridation of sapphire. Effect on the optical properties of GaN epitaxial overlayers

Abstract: GaN layers were grown by gas‐source molecular beam epitaxy on sapphire substrates using ammonia as a nitrogen source. The nitridation of an Al2O3 surface prior to the GaN growth was followed in situ by reflection high‐energy electron diffraction. A strong variation of the surface lattice parameter was observed corresponding to the formation of an AlN relaxed layer. The nucleation of GaN on such a nitridated surface is facilitated, as checked by atomic force microscopy. Optimization of the nitridation procedure is achieved by investigating the photoluminescence properties of GaN thin films grown for different nitridation times. It is found that the band‐edge and the yellow‐band luminescences are strongly dependent on the nitridated starting surface. Finally, the optimized nitridation process is used to grow high‐quality GaN epitaxial layers.

Monte Carlo simulation of In surface segregation during the growth of InxGa1-xAs on GaAs(001)

Abstract: The In surface segregation during the growth of InxGa1-xAs on GaAs(001) has been investigated through a Monte Carlo simulation taking into account the difference between the binding energies of InAs and GaAs and the effect of the epitaxial strain. Photoluminescence energies of quantum-well structures calculated from simulated composition profiles obtained at different temperatures are found to be in good agreement with the experimental ones. It is shown that Monte Carlo simulation is a very powerful way to predict the variation of the In composition profile as a function of growth parameters. It can, moreover, be easily extended to different materials, strain conditions, and surface morphologies.

Real‐time investigation of In surface segregation in chemical beam epitaxy of In0.5Ga0.5P on GaAs (001)

Abstract: Surface segregation processes during the growth of Ga0.5In0.5P/GaAs heterostructures by chemical beam epitaxy have been investigated in real time using reflection high‐energy electron diffraction (RHEED). It is shown that In segregation occurs at both GaInP on GaAs and GaAs on GaInP interfaces. Resulting composition profiles are deduced from the RHEED data.

Kinetics of surfactant-mediated epitaxy of iii-v semiconductors

Abstract: Surfactant-mediated epitaxy (SME) of III-V semiconductors is studied in the case of the GaAs(001) growth using Te as surfactant To account for the strong surface segregation of Te, a phenomenological exchange mechanism is used This process explains the reduction of the surface diffusion length evidenced by scanning tunneling microscopy (STM) However, this kinetics effect is observed only for restricted growth conditions: the As surface coverage should be sufficient to allow the exchange process STM results as well as Monte Carlo simulations clearly show that the group-V element surface coverage plays a key role in the kinetics of SME of III-V semiconductors

Luminescence and reflectivity of GaN/sapphire grown by MOVPE, GSMBE and HVPE

Abstract: This work presents an optical characterization by luminescence and reflectivity of GaN layers grown on sapphire using MOVPE, HVPE and GSMBE. Well resolved optical spectra are obtained for each growth technique. The luminescence of Mg doped MOVPE grown GaN is also studied. A Mg acceptor optical depth of ~ 260 meV is obtained.

Characterization of Near Edge Optical Transitions in Undoped and Doped GaN/Sapphire Grown by MOVPE, HVPE, and GSMBE

Abstract: The authors report a comparative study by luminescence and reflectivity of GaN grown on sapphire by MOVPE, HVPE and GSMBE. Whatever the growth technique, undoped GaN shows well resolved reflectivity spectra, allowing hetero-epitaxial strain to be taken into account in the interpretation of luminescence spectra. MOVPE provides the highest purity samples so far. From the luminescence study of n- and p-type doped samples, activation energies of 265 {+-} 10 meV and 34 {+-} 2 meV are deduced for Mg acceptors and Si donors respectively. From the luminescence spectra of HVPE grown samples, the presence of a perturbed interfacial n{sup +} layer is evidenced.

Effect of the Nitridation of the Sapphire (0001) Substrate on the GaN Growth

Abstract: The analysis of the sapphire surface nitridation by in situ reflection high-energy electron diffraction evidences the formation of a relaxed AlN layer. Its role on the early stage of the GaN growth is investigated by transmission electron microscopy (TEM). GaN crystallites of high structural quality, with the c-axis perpendicular to the sapphire basal plane, are observed when the starting surface is nitridated. On the other hand, the growth of GaN on a bare substrate involves the formation of larger islands with numerous defects. TEM study reveals that the c axis of these latter crystallites is systematically tilted by about 19{degree} with respect to the sapphire basal plane. Actually, this orientation corresponds to a particular epitaxial relationship between GaN and sapphire (0001) substrates. Finally, the optical properties of GaN thin layers are shown to be strongly dependent on the nitridation state of the sapphire surface.