Showing papers by "Eric Tournié published in 1994"

Interplay between Surface Stabilization, Growth Mode and Strain Relaxation during Molecular-Beam Epitaxy of Highly Mismatched III-V Semiconductor Layers

Abstract: We demonstrate that the surface stabilization provides an intrinsic means to control the growth mode and to delay strain relaxation during molecular-beam epitaxy of highly mismatched III-V semiconductor layers. Islanding is totally inhibited, the pseudomorphic regime is extended and the strain relief is impeded during growth of InAs single layers on (100)-GaAs substrates by changing the surface stabilization from anion- to cation-stable. We propose that maintaining a highly reactive surface provides a general means to kinetically restrict a system and to prevent islanding during heteroepitaxy.

Growth mechanism of GaAs on (110) GaAs studied by high‐energy electron diffraction and atomic force microscopy

Abstract: Using in situ reflection high‐energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM) we have studied the homoepitaxial growth on the (110) surface of GaAs. RHEED intensity oscillations indicate a layer‐by‐layer growth mode. The RHEED intensity oscillation frequency, however, decreases at a constant Ga flux with increasing substrate temperature and decreasing As flux, resulting in a lower apparent growth rate. AFM images of the surfaces reveal that at low As pressures large triangular shaped islands that ultimately lead to a rough surface are formed. The size and height of the islands increase and their density decreases with decreasing As pressures. In the area between the islands up to 1 μm large islands and terraces of monolayer height are found. The AFM images indicate that growth via step‐propagation on the islands and the monolayer stepped areas between the islands, not contributing to RHEED intensity oscillations, can account for the decrease in the apparent growth rate. For very low growth rates surface roughening due to island formation during growth is completely suppressed, resulting in a well ordered terraced surface with monolayer high steps and up to 0.5 μm large terraces that are due only to the unintentional 0.04° misorientation of the substrates. The formation of these large terrace sizes is due to the surprisingly large diffusion length of the Ga on the (110) surface.

Influence of the Growth Mode on the Microstructure of Highly Mismatched InAs/GaAs Heterostructures

Abstract: The lattice defect structures at highly mismatched InAs/GaAs interfaces are studied by transmission electron microscopy. The InAs films are grown by molecular beam epitaxy under various conditions resulting in different growth modes which strongly affect the relaxation process. In the Stranski-Krastanov mode, the strain is relieved first by formation of coherent islands and then by misfit dislocation generation near the interface. On the contrary, during two-dimensional growth only pure edge-type dislocations forming an orthogonal network directly at the interface are detected.

Strained InAs/Ga0.47In0.53As quantum-well heterostructures grown by molecular-beam epitaxy for long-wavelength laser applications

Abstract: Strained InAs single quantum wells (SQWs) embedded in a Ga 0.47 In 0.53 As matrix are studied by photoluminescence spectroscopy. Spontaneous emission is obtained up to 2.4 μm at 300 K, which is the longest wavelength achieved so far with QWs grown on InP substrates. Laser diodes based on a 10 ML wide InAs SQW confined by Ga 0.47 In 0.53 As layers are characterized. At 80 K the emission spectrum of broad area diodes is centered at 1.836 μm and the threshold current density is 475 A/cm 2 . Continuous wave operation is achieved with narrow stripe devices but at shorter wavelength due to increased losses and filling of the QW energy levels.

Defect control in highly mismatched III-V semiconductor heterostructures through virtual-surfactant-mediated molecular beam epitaxy

Abstract: The influence of the (100) InAs surface stoichiometry (As- or In-stable) on the growth mode and hence on strain relaxation is studied during MBE of strained InAs/Ga047In053As/InP and InAs/GaAs heterostructures Under conventional As-stable conditions, InAs grows in the Stranski-Krastanov mode, while under In-stable conditions InAs grows in the layer-by-layer mode whereby islanding is totally inhibited and the critical layer thickness is strongly increased The In-stable surface has thus a similar effect as a surfactant on the growth mode of strained InAs films This tunability of the growth mode makes feasible an efficient control of defect formation in highly mismatched semiconductor heterostructures, as the distinct growth mode determines the actual relaxation processes Our results open a new route for the synthesis of strained-layer heterostructures of superior structural perfection and optical properties

Surfactant-mediated molecular-beam epitaxy of highly-strained III-V semiconductor heterostructures

Abstract: The epitaxial growth of strained-layer heterostructures (SLHs) is currently under intense investigation, driven by the desire to obtain new physical properties different from those of the individual constituents of the structure. Much work is directed toward controlling the epitaxial morphology, i.e. the growth mode, of strained layers because this eventually governs the properties of SLHs. Surfactant-mediated molecular-beam epitaxy (SM-MBE) is a technique recently developed to face this challenge. We summarize the main results achieved with this approach in the field of III-V SLHs. >

Time‐resolved investigations of excitonic recombination in highly strained InAs/Al0.48In0.52As quantum wells

Abstract: We have investigated the exciton dynamics in strained InAs/Al048In052As quantum wells with well thicknesses of 2, 4, and 5 monolayers by time‐resolved photoluminescence spectroscopy Temperature‐dependent measurements of the decay time reveal a significant drop of the decay time above a critical temperature which depends on the well width The simultaneous measurement of the decay time and the integrated photoluminescence intensity enables us to estimate the radiative time constant As can be shown from the temperature dependence of the decay time nonradiative processes become more and more important at higher temperatures The strong increase of the radiative lifetime at higher temperatures is attributed to a thermal ionization of the excitons