Characterization of semiconductor laser gain media by the segmented contact method

Blood, P.; Lewis, G.M.; Smowton, Peter M.; Summers, Huw D.; Thomson, J.D.; Lutti, J.

doi:10.1109/jstqe.2003.819472

Cited by 196 publications

(152 citation statements)

References 14 publications

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“…We perform measurements of the optical loss ͑absorption and internal optical mode loss͒ using the multisection method 21 under reverse bias. The reverse bias is necessary to remove holes from the structure, provided by the dopants, that are otherwise captured by the dots and block the measurement of absorption that reflect the states that are present in the structure.…”

Section: Experimental Methods and Resultsmentioning

confidence: 99%

“…This suggests that the presence of the acceptor ions has not significantly affected the electronic states within the samples, even though previous work has suggested that the presence of free carriers during growth can affect the interdiffusion of the dots and surrounding material. 23 Having established that the samples are extremely similar except for the level of p doping we use the multisegment method 21 to measure the net modal gain spectra as a function of drive current density. A set of spectra with transverse electric ͑TE͒ polarization is shown in Fig.…”

Section: Experimental Methods and Resultsmentioning

confidence: 99%

“…To discover the reason for this we have determined the nonradiative current density as a function of the transparency point for each sample. The nonradiative current density is calculated by removing the spontaneous current density, which is also derived from the multisection experiment, 21 from the total current density ͑stimulated emission is negligible 21 in this segmented contact experiment͒. The data are plotted in Fig.…”

Section: Experimental Methods and Resultsmentioning

confidence: 99%

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Gain in p-doped quantum dot lasers

Smowton

Sandall

Liu

et al. 2007

Journal of Applied Physics

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We directly measure the gain and threshold characteristics of three quantum dot laser structures that are identical except for the level of modulation doping. The maximum modal gain increases at fixed quasi-Fermi level separation as the nominal number of acceptors increases from 0 to 15 to 50 per dot. These results are consistent with a simple model where the available electrons and holes are distributed over the dot, wetting layer, and quantum well states according to Fermi-Dirac statistics. The nonradiative recombination rate at fixed quasi-Fermi level separation is also higher for the p-doped samples leading to little increase in the gain that can be achieved at a fixed current density. However, we demonstrate that in other similar samples, where the difference in the measured nonradiative recombination is less pronounced, p doping can lead to a higher modal gain at a fixed current density.

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Section: Experimental Methods and Resultsmentioning

confidence: 99%

Section: Experimental Methods and Resultsmentioning

confidence: 99%

Section: Experimental Methods and Resultsmentioning

confidence: 99%

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Gain in p-doped quantum dot lasers

Smowton

Sandall

Liu

et al. 2007

Journal of Applied Physics

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“…Note that the current density associated with stimulated emission is negligible in this single pass experiment. 9 The amount of nonradiative recombination at each temperature, at injection levels to achieve a net modal gain of 6 cm −1 , is plotted in Fig. 4 for the p-doped sample.…”

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confidence: 99%

Temperature dependence of threshold current in p-doped quantum dot lasers

Sandall

Smowton

Thomson

et al. 2006

Applied Physics Letters

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The authors measure the temperature dependence of the components of threshold current of 1300 nm undoped and p-doped quantum dot lasers and show that the temperature dependence of the injection level necessary to achieve the required gain is the largest factor in producing the observed negative T 0 in p-doped quantum dot lasers. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2361167͔ p-type modulation doped In͑Ga͒As quantum dot lasers have attracted much interest recently, partially due to reports of an infinite or negative characteristic temperature ͑T 0 ͒ around room temperature. 1-3 Several authors have attributed this behavior to the temperature dependence of the Auger recombination process in doped structures, 2,4,5 although the particulars of the explanation varied in each case. In this work we report on measurements made on both intrinsic and p-doped quantum dot structures that emit at 1.3 m. From studying the radiative and nonradiative components of the threshold current we show that the temperature performance of p-doped lasers can be described without needing to consider Auger recombination.Two samples were grown by solid source molecular beam epitaxy on 3 in. n + ͑100͒ GaAs substrates. The devices were nominally identical except for the level of modulation doping. The active region consisted of five dot-in-a-well ͑DWELL͒ repeats, where each DWELL was made up of 3.0 ML of InAs grown on 2 nm of In 0.15 Ga 0.85 As and then capped by a further 6 nm of In 0.15 Ga 0.85 As, and these were then separated by 50 nm GaAs spacers. The active region was incorporated into a GaAs-Al 0.4 Ga 0.6 As waveguide structure. The lower n-contact region was doped with Si at 5 ϫ 10 18 cm −3 while the upper p contact was doped with Be at 5 ϫ 10 17 cm −3 , the p contact was finished with a 300 nm layer of GaAs doped at 1 ϫ 10 19 cm −3 . The growth temperature for the cladding layers was 620°C, while the InAs layers were grown at 510°C, the GaAs spacers were grown in two temperature steps; the first 15 nm at 510°C and the final 35 nm at 580°C, forming the so called high growth temperature spacer layers. 6 The doping consisted of Be atoms incorporated over a 6 nm region of GaAs situated 9 nm below each DWELL at a concentration of either 0 or 7.5 ϫ 10 17 cm −3 corresponding to either 0 or 15 acceptor atoms per quantum dot. Previous work on these structures has shown that the absorption spectra, and therefore the quantum dot states, are the same for the two structures. 7The threshold current was measured as a function of temperature on 2000 m long, 50 m wide oxide stripe lasers for both structures under pulsed conditions with a pulse length of 400 ns and a repetition rate of 1 kHz to avoid any self-heating, and this is shown in Fig. 1. The undoped structure shows a monotonically increasing threshold current from low to high temperatures as is normally observed for undoped quantum dot and quantum well structures. The p-doped structure exhibits a threshold current density that decreases as the temperature increases from 200 K r...

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“…14 At the dot densities necessary to achieve useful gain ($3 Â 10 10 cm À2 ), the limiting processes are capture and emission rather than carrier transport, 15 and rate equations for interaction with a thermal phonon bath describe the transition from random to thermal regimes 16 and give a good quantitative description of the temperature dependence of threshold current. 17,18 Photoluminescence spectra provide valuable insight into carrier distributions; 19,20 however, to relate such observations directly to laser operation, we have used electrically pumped measurements of gain and calibrated spontaneous emission spectra on a device structure, 21 which can be referenced to a known gain (the optical loss of the laser) to quantify the internal excitation. We observe that at temperatures below the minimum in threshold, the emission spectra broaden and analysis of the emission data at 20 K shows ground states in different size dots are populated with equal probability, increasing with drive current, indicative of random behaviour.…”

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confidence: 99%

Femtosecond pulse generation in passively mode locked InAs quantum dot lasers

Finch¹,

Blood²,

Smowton³

et al. 2013

Applied Physics Letters

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Optical pulse durations of an InAs two-section passively mode-locked quantum dot laser with a proton bombarded absorber section reduce from 8.4 ps at 250K to 290 fs at 20 K, a factor of 29, with a corresponding increase in optical bandwidth. Rate equation analysis of gain and emission spectra using rate equations suggests this is due to the very low emission rate of carriers to the wetting layer in the low temperature, random population regime which enables dots across the whole inhomogeneous distribution to act as independent oscillators. (C) 2013 AIP Publishing LLC

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Characterization of semiconductor laser gain media by the segmented contact method

Cited by 196 publications

References 14 publications

Gain in p-doped quantum dot lasers

Gain in p-doped quantum dot lasers

Temperature dependence of threshold current in p-doped quantum dot lasers

Femtosecond pulse generation in passively mode locked InAs quantum dot lasers

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