C. Rigo

On the mechanisms of strain release in molecular‐beam‐epitaxy‐grown InxGa1−xAs/GaAs single heterostructures

Inx Ga1−x As/GaAs single heterostructures have been grown by molecular‐beam epitaxy with different growing rates and In molar fractions. Indium composition, layer thickness, and residual strain have been measured mainly by Rutherford backscattering/channeling spectrometry and the results on selected samples compared with the results of other techniques like Auger electron spectroscopy and single‐ and double‐crystal x‐ray diffraction. Cathodoluminescence, x‐ray topography, transmission electron microscopy, and ion dechanneling have been employed to observe dislocations and to characterize their nature and density. While the onset of misfit dislocations has been found to agree with the predictions of the equilibrium theory, the strain release has been found to be much lower than predicted and the results are compared with the available metastability or nucleation models. Present results are in best agreement with nucleation models. Moreover, annealing experiments show that these heterostructures are at (or ...

STRUCTURAL AND OPTICAL INVESTIGATION OF INASXP1-X/INP STRAINED SUPERLATTICES

We report a complete characterization of InAsxP1−x/InP (0.05<x<0.59) superlattices epitaxially grown by low pressure metalorganic chemical vapor deposition and by chemical beam epitaxy. Samples were obtained by both conventional growth procedures and by periodically exposing the just-grown InP surface to an AsH3 flux. Using the latter procedure, very thin InAsxP1−x/InP layers (10–20 A) are obtained by P↔As substitutions effects. Arsenic composition of the so obtained layers depends both on AsH3 flux intensity and exposure times. Samples have been characterized by means of high resolution x-ray diffraction, high resolution transmission electron microscopy, 4 K photoluminescence, and extended x ray absorption fine structure spectroscopy. The combined use of high resolution x-ray diffraction and of 4 K photoluminescence, with related simulations, allows us to predict both InAsP composition and width, which are qualitatively confirmed by electron microscopy. Our study indicates that the effect of the formatio...

Investigations on the interface abruptness in CBE-grown InGaAs/InP QW structures

In this work we present a detailed analysis of chemical beam epitaxy-grown (CBE) InGaAs/InP multi quantum well (MQW) interfaces to explain experimental data from high quality single and multi-QWs. Our results compare well with the best published data we have obtained some outstanding results. For example, the very intense absorption peak and the high number of satellite peaks in the diffraction rocking curve, were obtained even on samples grown in non-optimized conditions. A careful use of growth interruption at the interfaces allows us to obtain monolayer (ml) interfaces. Nevertheless, the switching of the group V element at each interface leads to strain formation. This effect could become dramatic in superlattice structures with periods smaller than about 5 nm and barriers of less than 3–4 nm. More generally, the conditions for the growth of high quality single and multiple QWs is discussed in this work and these will be correlated with fourier transform photoluminesence (FTPL), high resolution x-ray diffraction (HRXRD), absorption, photo-absorption and photo-current (in PIN structures) measurements.

Influence of growth parameters on the interface abruptness in CBE-grown InGaAs/InP QWs and SLs

Abstract A simple thermodynamic model for As and P incorporation at the CBE-grown InGaAs/InP and InP/InGaAs interfaces has been developed. This model agrees with the X-ray diffraction and the photoluminescence features experimentally obtained from high-quality single quantum wells (SQWs) and multi-quantum wells (MQWs). Our experimental results compare well with the best published data and clearly show that monolayer interfaces can be obtained in this material system only by chosing the proper growth interruption (GI) conditions and accepting a strong mismatch at each interface. This effect could become dramatic in superlattice structures in which the QW period is smaller than 5 nm and the resulting strain could lead to poor crystal quality and optical properties.

The effects of roughness and composition variation at the InP/InGaAs and InGaAs/InP interfaces on CBE grown quantum wells

Abstract Quantum wells of the InGaAs/InP system grown with CBE and MOVPE techniques show compositional changes at the heterointerfaces. The interface layers (strained on the InP substrate) modify the energy profile of the well and the strain can be the cause of deviations from the simple layer-by-layer growth mechanism. Using FTPL, HREM and HRXRD characterization techniques, we will discuss the results of a model for the prediction of the InP/InGaAs/InP interface composition of CBE structures. The role of the growth interruption in order to obtain highly uniform QWs will be clearly emphasized.

Effect of InP substrate thermal degradation on MBE InGaAs layers

Abstract A common cleaning technique of InP substrates is the thermal in situ stabilization under As fluxes at the oxide desorption temperature. Since this desorption temperature is well above the upper limit of congruent sublimation, preferential desorption of phosphorus occurs with the formation of indium droplets. In the presence of arsenic flux these droplets precipitate as InAs crystallite with pyramidal habit which can be at the origin of the oval and whisker defects commonly reported in previous works.

BUTTERFLY BISTABILITY IN AN INGAAS/INP MULTIPLE-QUANTUM WELL WAVEGUIDE WITH DISTRIBUTED FEEDBACK

We report the experimental observation of butterfly bistability in an InGaAs/InP multiple‐quantum well waveguide with a distributed feedback grating, under cw operation and at sub‐milliwatt input power. Plasma effects on the excitonic optical properties in multiple‐quantum well structures are the basis of the observed bistability. Insight provided by a simple coupled‐mode description of the device and by many‐body theory of the field‐matter interaction is used both for device design and for interpretation of the results. In particular, the unconventional shape of the hysteresis is due to increased optical absorption at high injected optical power.

Two‐photon absorption in In1−x−yGaxAlyAs/InP waveguides at communications wavelengths

We have observed and measured two‐photon absorption in In1−x−yGaxAlyAs/InP waveguides grown by molecular beam epitaxy over the wavelength range of 1.5–1.65 μm. The values of β2, the two‐photon absorption coefficient, were 63 and 20 cm/GW for waveguides of compositions x=0.32, y=0.17 and x=0.15, y=0.31, respectively. These values are comparable with those predicted by scaling laws. We estimate the associated nonlinear refractive index coefficient n2 and discuss the implications for all‐optical switching.

Nonlinear contradirectional coupler

Results of room-temperature experiments with a multiple-quantum-well, nonlinear, contradirectional coupler are reported. A power-dependent, contradirectional coupling condition is demonstrated, inducing an optically controlled switching of optical signals, with a switching energy of 1 pJ.

Growth parameter optimization of short period ( < 50 Å) InGaAs/InP short period superlattices by chemical beam epitaxy for photonic devices

Abstract In this work, we describe the influence of the growth parameters on optical and crystallographic properties of InGaAs/InP short period superlattices (SPSLs). In particular, the optimized growth conditions applied for multi-quantum wells (MQWs) are no longer valid when the total period thickness is below 85 A and quasi-continuous growth interruption times are required. Structures with 31 A period thickness with excellent high resolution X-ray diffraction (HRXRD) and low temperature photoluminescence (PL) linewidth of 28 meV have been grown. Differential transmission spectra of barrier reservoir and quantum well electron transfer (BRAQWET) structures in which SPSLs substitute the corresponding quaternary (1.25 μm) layer show similar behaviour in the corresponding structures.