Determination of piezoelectric fields in strained GaInN quantum wells using the quantum-confined Stark effect

Takeuchi, Tetsuya; Wetzel, Christian; Yamaguchi, S.; Sakai, Hiromitsu; Amano, Hiroshi; Akasaki, Isamu; Kaneko, Y.; Nakagawa, Shigeru; Yamaoka, Yoshihisa; Yamada, Noriko

doi:10.1063/1.122247

Cited by 612 publications

(392 citation statements)

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“…In the air, where z ≤ 0, there is an incident probe pulse traveling toward the sample as well as a reflected pulse. The electric field in the air, E < (z, t), can thus be written as the sum (8) whereẼ i (z, t) andẼ r (z, t) are the slowly varying envelope functions of the incident and reflected probe fields, respectively. Inside the sample, z ≥ 0, the solution is given as…”

Section: Theorymentioning

confidence: 99%

“…2,3 These phonon oscillations were much stronger than folded acoustic phonon oscillations observed in other semiconductor superlattices. 4,5,6 InGaN/GaN heterostructures are highly strained at high In concentrations giving rise to large built-in piezoelectric fields, 7,8,9,10 and the large strength of the coherent acoustic phonon oscillations was attributed to the large strain and piezoelectric fields. 2 In this paper, we report the generation of strong localized coherent phonon wavepackets in strained layer In x Ga 1−x N/GaN epilayers and heterostructures grown on GaN and Sapphire substrates.…”

Section: Introductionmentioning

confidence: 99%

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Femtosecond pump-probe spectroscopy of propagating coherent acoustic phonons inInxGa1−xN∕GaNheterostructures

et al. 2005

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We show that large amplitude, coherent acoustic phonon wavepackets can be generated and detected in InxGa1−xN/GaN epilayers and heterostructures in femtosecond pump-probe differential reflectivity experiments. The amplitude of the coherent phonon increases with increasing Indium fraction x and unlike other coherent phonon oscillations, both amplitude and period are strong functions of the laser probe energy. The amplitude of the oscillation is substantially and almost instantaneously reduced when the wavepacket reaches a GaN-sapphire interface below the surface indicating that the phonon wavepackets are useful for imaging below the surface. A theoretical model is proposed which fits the experiments well and helps to deduce the strength of the phonon wavepackets. Our model shows that localized coherent phonon wavepackets are generated by the femtosecond pump laser in the epilayer near the surface. The wavepackets then propagate through a GaN layer changing the local index of refraction, primarily through the Franz-Keldysh effect, and as a result, modulate the reflectivity of the probe beam. Our model correctly predicts the experimental dependence on probe-wavelength as well as epilayer thickness.

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Section: Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Femtosecond pump-probe spectroscopy of propagating coherent acoustic phonons inInxGa1−xN∕GaNheterostructures

et al. 2005

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“…Their condensation into one macroscopic wave function 1,2 , however, is hampered by a couple of obstaclesto mention two of them, the fermionic substructure impairing the transition temperature 3,4 and the frequently fast radiative decay 5,6 . The latter can be cured by a spatial separation of the electron and hole subsystem, either using two coupled quantum wells with a superposed electric field 7,8 or by a single quantum well with a strong inherent electric field induced by the piezoand/or pyroelectricity of the crystal lattice [9][10][11][12] . Depending on the size of the vertical charge carrier separation, the excitons exhibit a significant dipole character, thus introducing repulsive dipoledipole interactions that hinder the formation of multiple exciton complexes.…”

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confidence: 99%

Manifestation of unconventional biexciton states in quantum dots

et al. 2014

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Although semiconductor excitons consist of a fermionic subsystem (electron and hole), they carry an integer net spin similar to Cooper-electron-pairs. While the latter cause superconductivity by forming a Bose-Einstein-condensate, excitonic condensation is impeded by, for example, a fast radiative decay of the electron-hole pairs. Here, we investigate the behaviour of two electron-hole pairs in a quantum dot with wurtzite crystal structure evoking a charge carrier separation on the basis of large spontaneous and piezoelectric polarizations, thus reducing carrier overlap and consequently decay probabilities. As a direct consequence, we find a hybrid-biexciton complex with a water molecule-like charge distribution enabling anomalous spin configurations. In contrast to the conventional-biexciton complex with a net spin of s ¼ 0, the hybrid-biexciton exhibits s ¼ ± 3, leading to completely different photoluminescence signatures in addition to drastically enhanced charge carrier-binding energies. Consequently, the biexcitonic cascade via the dark exciton can be enhanced on the rise of temperature as approved by photon cross-correlation measurements.

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“…Also there are large reported differences between theoretical and experimental results. 6 The majority of approaches to determine the internal field, have relied upon counteracting the quantum-confined Stark effect with an externally applied reverse bias and measuring properties of the quantum well as a function of this applied reverse bias. The reverse bias acts to oppose the internal field reducing the effect of the induced quantum confined Stark effect.…”

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confidence: 99%

Determination of the piezoelectric field in InGaN quantum wells

Brown

Pope

Smowton

et al. 2005

Applied Physics Letters

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In many studies, the value of the experimentally determined internal piezoelectric field has been reported to be significantly smaller than theoretical values. We believe this is due to an inappropriate approximation for the electric field within the depletion region, which is used in the analysis of experimental data, and we propose an alternative method. Using this alternative, we have measured the strength of the internal field of InGaN p-i-n structures, using reverse bias photocurrent absorption spectroscopy and by fitting the bias dependent peak energy using microscopic theory based on the screened Hartree-Fock approximation. The results agree with those using material constants interpolated from binary values. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1896446͔The internal field in GaN based quantum wells plays an important role in the operation of nitride-based light emitting diodes and lasers, affecting the emission wavelength, 1 the oscillator strength, 2 and the recombination lifetime, 3 hence an accurate value of the internal field is essential in understanding the properties of these devices. The internal field skews and breaks the symmetry of the well, causing spatial separation of the electron and hole wave functions and hence reduces the electron-hole overlap function. Reported values of the internal field 4,5 for the same nominal indium content vary by more than a factor of two, which is far greater than the expected error due to unintended variations in the indium content. Also there are large reported differences between theoretical and experimental results. 6 The majority of approaches to determine the internal field, have relied upon counteracting the quantum-confined Stark effect with an externally applied reverse bias and measuring properties of the quantum well as a function of this applied reverse bias. The reverse bias acts to oppose the internal field reducing the effect of the induced quantum confined Stark effect. At low bias, the well is skewed due to the internal field. At a critical bias, the contributions from the applied bias and the internal field are equal and opposite. In this case, the overlap of electron and hole wave functions and the ground state electron to heavy hole transition energy are maximized.The value of the externally applied bias to achieve flat band ͑"square-up" the quantum well͒ can then be used to obtain the internal field. The net internal field E in the well ͑E = 0 when the well is square͒ is related to the applied bias V using: 4where E int , L w , N, 0 , d d , and d u are the internal field, the quantum well width, the number of quantum wells, the built-in potential and the depletion and intrinsic widths, respectively. The width of the intrinsic region d u is given by the sum of the multiple well and barrier widths. The internal field E int , is the sum of the fields due to the piezoelectric effect and the spontaneous polarization. The first term of Eq. ͑1͒ is the background field written as the total voltage drop divided by the distance, over ...

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Determination of piezoelectric fields in strained GaInN quantum wells using the quantum-confined Stark effect

Cited by 612 publications

References 16 publications

Femtosecond pump-probe spectroscopy of propagating coherent acoustic phonons inInxGa1−xN∕GaNheterostructures

Femtosecond pump-probe spectroscopy of propagating coherent acoustic phonons inInxGa1−xN∕GaNheterostructures

Manifestation of unconventional biexciton states in quantum dots

Determination of the piezoelectric field in InGaN quantum wells

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