Internal Piezoelectric Field Research Articles

Excitation power and barrier width dependence of photoluminescence in piezoelectric multiquantum well p-i-n structures

Strained InGaAs/GaAs multiquantum well (MQW) structures grown on (111)B GaAs sub- strates incorporate strong internal piezoelectric fields. In contrast to (100)-oriented MQW p-i-n structures, the room temperature photoluminescence (PL) peak position and lineshape depend on the barrier width, which controls the ‘‘envelope field’’ across the MQW. The complex behavior of the PL peak position with excitation power results from a competition between screening of the well and envelope fields, and the photovoltaic effect.

Optical transitions involving excitons in quantum wires

We present a comprehensive discussion of the excitonic properties of V-shaped GaAs and InGaAs quantum wires grown on patterned substrates. Systematic linear and non-linear spectroscopic studies have been performed in order to clarify the impact of lateral confinement on the exciton wave function, namely: enhanced exciton binding energy, localization in magnetic field, recombination from excited states and multiphoton absorption. The careful evaluation of the electron confinement energies, based on the actual quantum wire profile obtained by TEM micrographs, including the internal piezoelectric field induced by off-diagnoal terms of strain tensor, reproduces quite well the measured one-dimensional states. Finally, application of quantum wires in a p-i-n wave guide for bistable operation is demonstrated.

SOME INVESTIGATIONS OF THE PHYSICAL PROPERTIES OF (Ga, In)As-GaAs HETEROSTRUCTURES GROWN WITH BUILT-IN PIEZOELECTRIC FIELD

The properties of single and double (Ga,ln)As-GaAs strained-layer quantum wells embedded in (pin) diodes are studied. These properties are found to be orientation-dependent, mainly due to the existence of a strong internal piezoelectric field in the (Ga,ln)As layers when the growth axis is polar. We first calculate how large the influences of the (pin) and piezoelectric field are to produce carrier tunnelling out of the active part of the heterostructure. This enables us to compute the carrier’s lifetime in the heterostructures and the corresponding resonance widths. Next, we compare the binding energies of interacting electron and hole pairs in double quantum wells with or without internal piezo electric fields. We show that the exciton binding energy is less sensitive to the piezoelectric field than the oscillator strength. Under photo excitation, many body-effects and bandgap renormalization can be easily produced in strained-layer quantum wells with internal built-in piezo-electric fields. We illuminated at low temperature single and double Ga 0.92 ln 0.08 As-GaAs strained layer quantum wells grown either along the (001) or (111) direction, and tuned over several decades the densities of photo-injected carriers. The comparison between experimental data and the results of a Hartree calculation including the space charge effects reveals that many body interactions are efficiently photo-induced in the (111)-grown samples. Moreover, we show that the tunnelling of the two lowest-lying heavy-hole levels can be stimulated for moderate carrier densities making such structures promissive in order to realise self electrooptic effect device (SEED) modulators.

Spontaneous and stimulated photoluminescence of CdSe/CdS Stark superlattices

Photoluminescence properties of CdSe/CdS intrinsic Stark superlattices are studied mainly by means of nanosecond optical spectroscopy. The blue-shift induced by increasing screening of the internal piezoelectric fields with increasing excitation power reaches nearly 0.4eV for samples with large periods. At excitation levels above 2 to 20MW/cm2 stimulated emission is observed depending on temperature. Measurements by the stripe-length method give gem maximum values around 103cm-1.

Structural and optical characterizations of InAsP/InP strained multiple quantum wells grown on InP (111)B substrates

InAsP/InP strained multiple quantum wells (MQWs) with specular surfaces were grown on InP (111)B substrates by gas-source molecular beam epitaxy. Cross-sectional transmission electron microscopy and high-resolution x-ray rocking curves show that the InAsP/InP (111)B MQW structures possess sharp and uniform interfaces, excellent periodicity, and crystalline quality. Structural parameters were extracted accurately from a dynamical-theory simulation by considering the anisotropy of the (111) strain tensor. Low-temperature photoluminescence and photoluminescence excitation measurements revealed interband excitonic transitions, and the energies agree with a calculation with an internal piezoelectric field taken into account.

Effects of an electric field on exciton recombination in three-step asymmetric coupled quantum wells

The radiative transitions of (100)- and (311)A-oriented three-step asymmetric coupled quantum wells in an electric field are studied by photoluminescence. Four distinct transitions are observed in the spectra which exhibit remarkably complex energy shifts with the applied field. It is shown that these transitions originate from the two pairs of spatially direct and indirect heavy-hole excitons in the three-step quantum well and that their electric-field dependence is dominated by the conversion of the direct into the indirect excitons and vice versa. Furthermore, we discuss the effects of the nonconventional crystal orientation and show that substantial modifications of the basic electro-optical properties can be achieved from internal piezoelectric fields incorporated within the structure.

Exciton binding energies and photo-induced tunnelling of carriers in (Ga,In)As-GaAs heterostructures grown with built-in piezoelectric field

We compare the binding energy of interacting electron and hole pairs in double quantum wells with and without internal piezo-electric fields. We show that the exciton binding is less sensitive to the piezo electric field than the oscillator strength. This allows many body-effects and bandgap renormalization to be easily produced in strained-layer quantum wells with internal built-in piezo-electric fields, under photo excitation. Our observation was made at low temperature by comparing the behaviour of Ga 0.92 In 0.08 gAs-GaAs strained layer single and double quantum wells grown along the (001) and (111) directions when the densities of photoinjected carriers are tuned over several decades. Comparison between experimental data and the results of a Hartree calculation including the space charge effects reveals that manybody interactions are efficiently photo-induced in the (111)-grown samples. Moreover, tunnelling of the two first excited heavy-hole levels can be stimulated for moderate carrier densities making such structure promissive for realising self electrooptic effect device (SEED) modulators

Observation of many-body effects and band-gap renormalization in low-dimensional systems with built-in piezoelectric fields.

We show that many-body effects and band-gap renormalization can be easily produced in strained-layer quantum wells with internal built-in piezoelectric fields, under photoexcitation. Our observation was made at low temperature by comparing the behavior of ${\mathrm{Ga}}_{0.92}$${\mathrm{In}}_{0.08}$As-GaAs strained-layer quantum wells grown along the (111) and (001) directions and tuning the densities of photoinjected carriers over several decades. Comparison between experimental data and the results of Hartree calculations including the charge space effects reveals that many-body interactions are photoinduced.

Optical properties of single and double (111)-grown (Ga, In)As-GaAs strained-layer quantum wells under strong photo-injection

We show that manybody-effects and bandgap renormalization can be easily produced in strained-layer quantum wells with internal built-in piezo-electric fields, under photo excitation. Our observation was made at low temperature by comparing the behaviour of Ga 0.92 In 0.08 As-GaAs strained layer single and double quantum wells grown along the (001) and (111) directions when the densities of photoinjected carriers is tuned over several decades. Comparison between experimental data and the results of a Hartree calculation including the space charge effects reveals that manybody interactions are efficiently photo-induced in the (111)-grown samples. Moreover, in the case of double quantum wells, additional transitions appear in the photoluminescence spectra, due to the tunnelling of the two first excited heavy-hole levels for moderate densities

Piezo-optical effects in GaAs with interspersed (211)-InAs lattice planes.

We study piezoelectric field effects in the ultimate atomic limit. The insertion of piezoelectrically active (211)-InAs lattice planes in GaAs gives rise to optical phenomena not observed in analogous (100) structures. The InAs-related luminescence exhibits a pronounced blue shift with increasing excitation density. The nonlinear dependence of the corresponding luminescence efficiency is a manifestation of the internal piezoelectric field in the strained InAs sheets.

Internal piezoelectric fields in GaInSb/InAs strained-layer superlattices probed by optically induced microwave radiation

Using a newly developed femtosecond electro-optic technique, a built-in electric field near a semiconductor surface can be measured by a contactless approach. We have observed for the first time equal strength but opposite direction of strain-induced piezoelectric fields from lattice-mismatched A face and B face of GaInSb/InAs strained-layer superlattices by optically induced microwave radiation.

Modulation of internal piezoelectric fields in strained-layer superlattices grown along the [111] orientation

Large internal piezoelectric fields are generated when strained-layer superlattices are grown from III–V zinc-blende-structure compound semiconductors. The orientation of these internal fields depends on the components of the strain tensor and, consequently, on the growth orientation of the superlattice. In the usual case of strained-layer superlattices grown along the [001] axis, the piezoelectric fields vanish. However, the case of strained-layer superlattices grown along the [111] axis is particularly interesting because the internal piezoelectric fields are parallel to the growth axis and their magnitude typically exceeds 100 kV/cm for lattice mismatches as small as 1%. Therefore, [111]-oriented strained-layer superlattices exhibit novel physical properties and present technological opportunities not afforded by commonly grown [001]-oriented strained-layer superlattices. The internal strain-induced fields substantially modify the electronic structure and optical properties of [111]-oriented strained-layer superlattices. The presence of such large strain-induced polarization fields in [111]-oriented strained-layer superlattices is a physically interesting and technologically significant feature because of the possibility of modulating these internal fields by the application of an external field. Examples of modulating fields include (i) screening by photogenerated free carriers, (ii) external electric bias, or (iii) applied uniaxial stress. As a consequence of these modulations, large nonlinear optic, electro-optic and piezo-optic effects result. These effects are illustrated by calculations performed for Ga1−xInxAs–Al1−yIny As strained-layer superlattices grown along the [111] axis.

Optical Absorption Studies of Plastically Deformed InSb

AbstractOptical absorption studies of edge‐type dislocations are carried out on n‐ and p‐type, weakly doped InSb. Edge‐type dislocations are selectively introduced by means of uniaxial compression at 220 °C. The presence of dislocation induces two main changes in the optical absorption spectra: i) absorption tails just before the band edge, which are associated with the strong internal piezoelectric fields and ii) reduction of the intraband absorption, which are explained by the presence of trapping levels bound to the dislocations.