Polarization effects in AlxGa1−xN / GaN superlattices

2000 ◽  
Vol 639 ◽  
Author(s):  
Erik L. Waldron ◽  
E. Fred Schubert ◽  
John W. Graff ◽  
Andrei Osinsky ◽  
Michael J. Murphy ◽  
...  
Keyword(s):  
Room Temperature ◽  
Stark Effect ◽  
Blue Shift ◽  
Transition Band ◽  
Polarization Effects ◽  
Quantum Confined Stark Effect ◽  
Free Carriers ◽  
Bulk Gan ◽  
Band Transition ◽  
Photoluminescence Studies

ABSTRACTRoom temperature and low temperature photoluminescence studies of AlxGa1−xN/GaN superlattices reveal a red shift of the dominant transition band relative to the bulk GaN bandgap. The shift is attributed to the quantum-confined Stark effect resulting from polarization fields in the superlattices. A theoretical model for the band-to-band transition energies based on perturbation theory and a variational approach is developed. Comparison of the experimental data with this model yields a polarization field of 4.6 × 105 V/cm for room temperature Al0.1Ga0.9N/GaN and 4.5 × 105 V/cm for room temperature Al0.2Ga0.8N/GaN. At low temperatures the model yields 5.3 × 105 V/cm for Al0.1Ga0.9N/GaN and 6.3 × 105 V/cm for Al0.2Ga0.8N/GaN. The emission bands exhibit a blue shift at high excitation densities indicating screening of internal polarization fields by photo-generated free carriers.

GaN Quantum Dots Grown at High Temperatures by Molecular Beam Epitaxy

2004 ◽  
Vol 831 ◽  
Author(s):  
Tao Xu ◽  
Adrian Williams ◽  
Christos Thomidis ◽  
Theodore D. Moustakas ◽  
Lin Zhou ◽  
...  
Keyword(s):  
Quantum Dots ◽  
High Temperatures ◽  
Stark Effect ◽  
Spatial Density ◽  
Height Distribution ◽  
Quantum Confined Stark Effect ◽  
Sapphire Substrates ◽  
Superlattice Structure ◽  
Bulk Gan ◽  
Photoluminescence Studies

ABSTRACTIn this paper we report the growth by MBE of GaN quantum dot superlattices (QDSLs) with AlN barriers on (0001) sapphire substrates at relatively high temperatures (770 °C) by the modified Stranski-Krastanov method. TEM studies indicate that the GaN QDs are truncated pyramids. We find that the height distribution of the dots depends strongly on the number of GaN monolayer coverage on the top of AlN. Specifically, we find that the height distribution consists of two Gaussian distributions (bimodal) for coverage of 3 and 4 MLs, and becomes single Gaussian distribution for 5 and 6 MLs of coverage. Furthermore, we find that the density of quantum dots increases with the degree of coverage and saturates at 2×1011 dots/cm2. The number of stacks in the superlattice structure was also found to lead to bimodal height distribution of the QDs. Ordering of the quantum dots was accomplished by thermal annealing of the sapphire substrates at 1400 °C prior to the growth of GaN QDs. The annealing process reveals the vicinal steps due to the miscut of the substrates and the GaN QDs were found to line up along those steps. Photoluminescence studies show a broad luminescence spectrum centered at 3 eV which is red shifted with respect to that of bulk GaN and is consistent with internal fields due to polarization (Quantum Confined Stark Effect). Furthermore, we find that the luminescence intensity increases with the number of stacks in the superlattice structure due to higher spatial density of QDs.

Photoluminescence studies of GaAs quantum wires with quantum confined Stark effect

1997 ◽  
Vol 70 (5) ◽  
pp. 646-648 ◽  
Author(s):  
T. Arakawa ◽  
Y. Kato ◽  
F. Sogawa ◽  
Y. Arakawa
Keyword(s):  
Stark Effect ◽  
Quantum Wires ◽  
Quantum Confined Stark Effect ◽  
Quantum Confined ◽  
Photoluminescence Studies

The Investigation of InGaN MQW Electroabsorption Modulator using the LED/Modulator/Detector Monolithically Integrated Structure

2000 ◽  
Vol 639 ◽  
Author(s):  
S.W. Chung ◽  
Y.S. Zhao ◽  
C.H. Lin ◽  
H.P. Lee
Keyword(s):  
Stark Effect ◽  
Piezoelectric Effect ◽  
Free Exciton ◽  
Stokes Shift ◽  
Blue Shift ◽  
Electroabsorption Modulator ◽  
Quantum Well Structures ◽  
Quantum Confined Stark Effect ◽  
Monolithically Integrated ◽  
Emission And Absorption Spectra

ABSTRACTThe strong piezoelectric effect and quantum confined stark effect (QCSE) in the InGaN/GaN quantum well structures allow one to modify the free exciton absorption by the extrinsic field. The QCSE is investigated using a monolithically integrated three-section device comprising an LED, electroabsorption modulator and a detector section. The experimental results show that the LED output can be modulated as indicated by the detector signal. The strength of modulation decreases monotonically with increasing In composition in the InGaN/GaN MQW. The result can be explained on the basis of the Stokes' shift between the emission and absorption spectra in the InGaN/GaN QW structure, and a blue shift of the absorption spectrum due to the QCSE as a result of the piezoelectric effect.

Structural and Optical Studies of InGaN/GaN Superlattices Implanted with Eu Ions

MRS Advances ◽  
2017 ◽  
Vol 2 (3) ◽  
pp. 179-187
Author(s):  
Jingzhou Wang ◽  
Venkata R. Thota ◽  
Eric A. Stinaff ◽  
Mohammad Ebdah ◽  
Andre Anders ◽  
...  
Keyword(s):  
Stark Effect ◽  
Annealing Temperature ◽  
Chemical Vapor ◽  
Blue Shift ◽  
Photoluminescence Spectra ◽  
Temperature Dependent ◽  
Optical Studies ◽  
Quantum Confined Stark Effect ◽  
Spectral Shifts ◽  
Before And After

ABSTRACTIn0.06Ga0.94N/GaN superlattices (SLs) grown on sapphire (0001) by metalorganic chemical vapor deposition were studied before and after europium (Eu) ion implantation to understand the strain induced-effects in the SL structure. The implanted SLs were investigated as a function of the thermal annealing temperature up to 1000 °C in nitrogen ambient. Temperature dependent photoluminescence spectra showed a red-shift of the SL emission peaks due the quantum confined Stark effect, followed by a blue-shift due to In atoms out-diffusion from the In0.06Ga0.94N quantum well, for both Eu ions implanted and unimplanted SLs. The amplitude of observed spectral shifts was smaller and the line width of the SLs emission peaks were narrower in the SLs:Eu3+ as compared to the unimplanted SLs. It is concluded that Eu3+ ions modified the strain in the SLs acting like impurity and/or defects getter in implantation degraded SLs resulting in material phase purification and improvements of SLs optical properties.

Nano-Photoluminescence Studies of Self-Assembled Quantum Dots

1999 ◽  
Vol 583 ◽  
Author(s):  
H. Htoon ◽  
Hongbin Yu ◽  
D. Kulik ◽  
J. W. Keto ◽  
O. Baklenov ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Stark Effect ◽  
Nanometer Scale ◽  
Far Field ◽  
Quantum Confined Stark Effect ◽  
Carrier Transfer ◽  
Field Dependent ◽  
Self Assembled ◽  
Photoluminescence Studies ◽  
Individual Self

AbstractTwo simple and effective far-field-optics-based methods capable of isolating photoluminescence peaks of different individual self assembled quantum dots (SAQD's) with nanometer scale precision are presented. By using these methods, we performed the temperature and electric field dependent studies on the optical properties of SAQD's. We found temperature induced inter-dot carrier transfer among neighboring quantum dots (QD's) and observed the quantum confined stark effect (QCSE).

Spontaneous and Stimulated Recombination in the Nitrides

1996 ◽  
Vol 449 ◽  
Author(s):  
A. Hangleiter ◽  
F. Scholz ◽  
V. Härle ◽  
J. S. Im ◽  
G. Frankowsky
Keyword(s):  
Quantum Wells ◽  
Room Temperature ◽  
Optical Gain ◽  
Stimulated Emission ◽  
Time Resolved ◽  
Double Heterostructures ◽  
Bulk Gan ◽  
Photoluminescence Studies ◽  
Excitonic Effects ◽  
Time Resolved Photoluminescence

ABSTRACTBoth spontaneous and stimulated emission processes are essential ingredients for constructing a laser from the nitrides. Based on our picosecond time-resolved photoluminescence studies we show that spontaneous radiative recombination is strongly influenced by excitonic effects, both in bulk GaN and in quantum wells. Particularly in quantum wells, localization of excitons plays an important role. We have studied the optical gain spectra in GaInN/GaN and GaN/AlGaN double heterostructures and quantum wells, grown by LP-MOVPE, using the stripe excitation method. Both room temperature and low temperature measurements were performed. Based on our results, we discuss the physical mechanism of optical gain in the nitrides as well as consequences for laser operation. We show that localization or, equivalently, the formation of quantum dot like structures, governs the optical gain mechanism in the nitrides.

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