Optical Gain of CdSe Quantum Dot Stacks

Sebald, K.; Michler, Peter; Gutowski, J.; Kröger, Roland; Passow, T.; Klude, M.; Hommel, D.

doi:10.1002/1521-396x(200204)190:2<593::aid-pssa593>3.0.co;2-4

Cited by 19 publications

(13 citation statements)

References 16 publications

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“…The QD density was of the order 10 10 -10 11 cm --2 . The photoluminescence spectra exhibited a 100 meV broad emission line at 2.35 eV, caused by the superposition of single lines of the QD ensemble [58].…”

Section: Cdse Quantum-dot Laser Structuressupporting

confidence: 54%

Excitons in Wide-Gap Semiconductors: Coherence, Dynamics, and Lasing

Gutowski

Michler

Rückmann

et al. 2002

phys. stat. sol. (b)

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The role of excitonic excitations in wide-gap II-VI and nitride semiconductors is reviewed with focus on the recent research at Bremen University. More-particle excitations such as trions and biexcitons are studied including their contributions to nonlinearities in the coherent regime and to lasing. Specific questions concerning laser processes in wide-gap materials are addressed. IntroductionWide-gap semiconductors such as most of the Zn and Cd based II-VIs or the nitride based blue to UV emitters are model materials for exciton and Coulomb correlation effects on the whole time and a large intensity scale since excitons in these compounds are much more stable as in conventional III-V semiconductors widely used for optoelectronic applications so far. This in particular holds for lower-dimensional structures exhibiting exciton binding energies exceeding those of the optical phonons. Thus, even at high electron-hole densities and rather elevated temperatures, lasing is still strongly governed by Coulomb correlation effects [1,2], what makes wide-gap materials rather different from III-Vs concerning this important aspect of application. Also with respect to very basic phenomena such as higher-order contributions to coherent multi-wave mixing, or propagation effects, the role of exciton correlation is extremely significant [3][4][5][6][7]. This paper is a short review of the recent activities of the Bremen group in the above-mentioned fields.

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Section: Cdse Quantum-dot Laser Structuressupporting

confidence: 54%

Excitons in Wide-Gap Semiconductors: Coherence, Dynamics, and Lasing

Gutowski

Michler

Rückmann

et al. 2002

phys. stat. sol. (b)

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“…InGaN QWs reach values of g mod = 180 -300 cm -1 and L s = 250 -350 µm [21]. However, as the QD density is taken into account by calculating the modal gain per QD, it is found that our results are comparable with established materials [11], yielding 10 -9 cm -1 per QD. This gives evidence to the fact that rather the surrounding structure needs further improvement as well as the filling factor being still very low.…”

Section: Resultssupporting

confidence: 83%

“…This may be due to the fact that the QD layers contain much less active material than QW structures, since the QD density is limited to 5×10 9 cm -2 per layer. For CdSe QD stacks containing five layers with a QD density of up to 10 11 cm -2 per layer, stimulated emission was demonstrated for 32 to 60 kW/cm -2 [11] while threshold densities of below 1kW/cm -2 were recently reported for arsenide based structures at room temperature [22]. The modal gain of the waveguide structure is investigated via the VLS method.…”

Section: Sample Structure and Experimental Setupmentioning

confidence: 99%

“…However, it is necessary to increase the QD density by using stacked layers to achieve sufficient active material for appropriate lasing operation. This method has been very successful for the group-III arsenides [9,10] and the II-VI wide bandgap semiconductors [11]. In addition, stacking of the QD layers is expected to result in an increasing uniformity of the QD size throughout the layering process [12], resulting in an increasing modal gain [13].…”

Section: Introductionmentioning

confidence: 99%

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Optical properties and modal gain of InGaN quantum dot stacks

Kalden

Sebald

Gutowski

et al. 2009

Phys. Status Solidi (c)

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We present investigations of the optical properties of stacked InGaN quantum dot layers and demonstrate their advantage over single quantum dot layer structures. Measurements were performed on structures containing a single layer with quantum dots or threefold stacked quantum dot layers, respectively. A superlinear increase of the quantum dot related photoluminescence is detected with increasing number of quantum dot layers while other relevant GaN related spectral features are much less intensive when compared to the photoluminescence of a single quantum dot layer. The quantum dot character of the active material is verified by microphotoluminescence experiments at different temperatures. For the possible integration within optical devices in the future the threshold power density was investigated as well as the modal gain by using the variable stripe length method. As the threshold is 670 kW/cm 2 at 13 K, the modal gain maximum is at 50 cm -1 . In contrast to these limited total values, the modal gain per quantum dot is as high as 10 -9 cm -1 , being comparable to the II-VI and III-As compounds. These results are a promising first step towards bright low threshold InGaN quantum dot based light emitting devices in the near future.

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“…Our T 0 measurements agree well with T 0 measurements for MBE grown CdSe QD stacks that also show two distinct regions with similar T 0 values. 31 This corresponds with the prediction for high T 0 values in 0-D systems. In an ideal 0-D system, T 0 should approach infinity due to the discrete density of states.…”

Section: Resultsmentioning

confidence: 99%

Temperature Dependence of Optical Gain in CdSe/ZnS Quantum Rods

et al. 2007

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We studied the optical gain characteristics of CdSe/ZnS core/shell colloidal quantum rods, investigated their temperature dependence, and compared the gain properties with quantum dots (QD). The gain was measured systematically for close-packed films of rods and dots under quasi-CW nanosecond optical pumping, using the variable stripe length method measuring the amplified spontaneous emission (ASE). Tunable ASE can be achieved by changing the rod diameter. Optical gain factors of up to 350 cm -1 at a temperature range of 10-120 K were measured for quantum rods. Above 120 K, the gain decreased sharply, but by increasing the pump power, ASE was easily achieved also at room temperature. The temperature dependence was assigned to the Auger heating process and phonon assisted thermal relaxation. QD of similar diameters as the rods showed much smaller gain values (∼50 cm -1 ) and a sharp decrease in gain at lowered temperatures (∼50 K), and ASE could not be detected at room temperature even at high pump powers. The significantly improved gain values in quantum rods as compared with dots were attributed to the slower Auger relaxation rates, the higher absorption cross-section, and the reduced self-absorption due to the larger Stokes shift. The temperature dependence of the threshold power for the quantum rods, used to characterize the thermal insensitivity of the system, showed two distinct temperature regions. In the low-temperature region, a very high T 0 value of 3500 K was measured, as predicted for a low-dimensional quantum confined system.

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Optical Gain of CdSe Quantum Dot Stacks

Cited by 19 publications

References 16 publications

Excitons in Wide-Gap Semiconductors: Coherence, Dynamics, and Lasing

Excitons in Wide-Gap Semiconductors: Coherence, Dynamics, and Lasing

Optical properties and modal gain of InGaN quantum dot stacks

Temperature Dependence of Optical Gain in CdSe/ZnS Quantum Rods

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