The quantum confined Stark effect in InAs/InGaAs QDs using an undoped and p-modulation doped active region was investigated. Doping potentially offers more than a 3x increase in figure of merit modulator performance up to 100°C

Abadía, N

Allford, C

Jarvis, L

Liu, H

Maglio, B

Mahoney, J

Shutts, S

Smowton, PM

Tang, M

English

UCL Discovery

QCSE and Carrier Blocking in P-modulationDoped InAs/InGaAs Quantum DotsJoe Mahoney1, Peter M Smowton1, Benjamin Maglio1, Lydia Jarvis1, Craig Allford1,Samuel Shutts1, Mingchu Tang2, Huiyun Liu2, and Nicolás Abadı́a1,∗1 School of Physic and Astronomy, Cardiff University, Queens Building, The Parade, Cardiff CF24 3AA, UK2 Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, UKAbstract: The quantum confined Stark effect in InAs/InGaAs QDs using an undoped andp-modulation doped active region was investigated. Doping potentially offers more than a 3xincrease in figure of merit modulator performance up to 100 ◦C. © 2020 The Author(s)1. IntroductionQuantum dot (QD) devices have gathered interest for many reasons, like having the potential to be grown oversilicon with little degradation in device performance [1]. InAs/In(Ga)As quantum dot (QD) devices have receiveda lot of attention in recent years due to their potential to bring efficient lasers to the silicon photonics platform.However other optoelectrionic devices required for optoelectronic integration such as the QD modulator have notheavily studied [1]. The need for high performance, low power modulator devices can be realised through the use ofthe quantum confined Stark effect (QCSE) and has been demonstrated in both QDs and quantum wells (QW) [2, 3].The influence of doping in QWs has been studied in [4]. It was shown that the incorporation of a modulation-dopedsuperlattice in a multi-QW structure can lead to equivalent contrast ratios with a 1.8x reduction in applied voltage. Tothe best of our knowledge, there has been no direct comparison between the QCSE in equivalent doped and undopedQD active region stacks. Given the different nature of the states present in QDs, it is expected that modulation dopingmay lead to even further enhancements to electro-absorption modulator (EAM) performance [1]. QDs also offer thepromising prospect of greater temperature tolerance [5], and so here we present a comparison of two identical QDactive region stacks, except where p-modulation doping is present in one. We measure the QCSE in both stacks withtemperature to determine their potential performance as EAMs, and we show that the inclusion of the p-modulationdoping in the stack offers up to 3x larger figure of merit (FoM).2. ResultsThe segmented contact method was utilized to measure the QCSE in the QD active regions [6]. The active regionsused are similar to those we have already measured in [5]. The only difference in the current stack is that the dopedstack has a doping concentration in the QD active region of 10 holes per dot.Fig. 1: ∆α and α(1V ) for p-modulated doped (a) and undoped (b) multi-section devices vs temperature.The measurements are plotted in Fig. 1 and showcase the absorption at a reverse bias of 1V α(1V ) and changein absorption ∆α for both the doped and undoped active regions as a function of temperature. It can be seen whencomparing the two sets of α(1V ) data that unlike the undoped active region, the doped active region’s peak absorptionstrength increases slightly with increasing temperature. This behavior is attributed to the redistribution of carriersin the valence states at elevated temperatures making lower energy transitions more prominent, thus leading to anincrease in ground state transition strength. When comparing the ∆α of both the doped and undoped materials, thereis a slight decrease in peak ∆α with temperature from both active regions, with the undoped sample generally havingthe larger peak ∆α value of around 12 dBmm−1. Despite the larger ∆α in the undoped active region, it is important tocompare this with the α(1V ) to take into account the insertion loss. Hence, we have used the ratio of the ∆α to theα(1V ) as a FoM to compare the two active regions stacks. The FoM for both active regions using a 4V and 9V -swingsare presented in Fig. 2. They present a clear indication of the enhancement in active region performance of the dopedmaterial. It can be seen in Fig. 2 even up to 100 ◦C that the doped sample has almost a 3x enhancement in the FoMover the undoped sample for both voltage swings. The maximum FoM of the undoped stack is around 2.4 in Fig. 2bfor a 9V -swing. A very similar FoM can be achieved with a 4V -swing in the doped material as shown in Fig. 2a. Themaximum FoM is 8 for the doped stack and degrades with temperature to a value of 5 at 100 ◦C. Nevertheless, thedoped active region still works at high temperature and out performs the undoped stack by at least 2x over the wholetemperature range. This improvement in FoM is mainly attributed to state-filling effects that are present in the dopedFig. 2: FoM for a 9V -swing (a) and 4V -swing (b) for both doped and undoped QDs vs temperature.sample. Under the equivalent reverse bias, the doped sample exhibits an enhanced red shift. This red shift with voltagehas two contributions, the first being from the Stark shift, with the second originating from the removal of holes fromthe lowest valence states of the dots. When the doped active region has no external bias applied, the valence statesare filled with holes, thus suppressing absorption at the lowest energy dot states and skewing the observed absorptionspectrum to high energy. When a reverse bias is applied across the active region, the holes start to be depleted, thusleading to more absorption at lower energy. The reason for this is that the transitions from lower energy states are nowbecoming possible. This reduction in the carrier blocking effect is different to the reduction in excitonic screening thatoccurs in QWs [7], and as we have demonstrated more useful for modulators. The carrier depletion also leads to anincrease in absorption peak for ground state transitions in the doped stack while in the undoped one, the absorptionpeak decreases as expected from the QCSE. This effect is also a contributing factor to the improvement in FoM in thedoped stack.3. ConclusionWe have demonstrated the benefit of p-modulation doping in QD active regions by measuring the QCSE up to100 ◦C. These results demonstrate that p-modulation doping in QDs offer up to 3x improvement in the FoM. This willlead better optimised modulators that have an improved trade-off between the extinction ratio and insertion loss andcan potentially operate up to 100 ◦C.References1. J. C. Norman, D. Jung, Y. Wan, and J. E. Bowers, “Perspective: the future of quantum dot photonic integrated circuits,” APL Photon. 3,030901 20182. C. H. Lin, J. P. Wu, Y. Z. Kuo, Y. J. Chiu, T. E. Tzeng and T. S. Lay, ”InGaAs self-assembly quantum dot for high-speed 1300 nmelectroabsorption modulator”, J. Cryst. Growth, vol. 323, no. 1, pp. 473-476, 2011.3. S. A. Sobhani et al., ”Proposal for Common Active 1.3- µ m Quantum Dot Electroabsorption Modulated DFB Laser,” in IEEE PhotonicsTechnology Letters, vol. 31, no. 6, pp. 419-422, 15 20194. M. C. L. Areiza, C. V. -. Tribuzy, S. M. Landi, M. P. Pires and P. L. Souza, ”Amplitude Modulators containing an nipi delta dopingsuperlattice,” in IEEE Photonics Technology Letters, vol. 17, no. 10, pp. 2071-2073, 20055. E. D. Le Boulbar et al., ”Temperature Dependent Behavior of the Optical Gain and Electroabsorption Modulation Properties of anInAs/GaAs Quantum Dot Epistructure,” 2019 21st International Conference on Transparent Optical Networks 20196. P. Blood, G. M. Lewis, P. M. Smowton, H. Summers, J. Thomson and J. Lutti, ”Characterization of semiconductor laser gain media by thesegmented contact method,” in IEEE Journal of Selected Topics in Quantum Electronics, vol. 9, no. 5, pp. 1275-1282, 20037. R. Prasanth, J. E. M. Haverkort and J. H. Wolter, ”Compact polarization-independent Mach-Zehnder space switch combining carrierdepletion and the quantum confined Stark effect,” in IEEE Journal of Quantum Electronics, vol. 39, no. 2, pp. 379-383, 2003

QCSE and carrier blocking in P-modulation doped InAs/InGaAs quantum dots

https://discovery.ucl.ac.uk/10139868/1/QCSEAndCarrierBlockingInPModulationDopedInAs-InGaAsQuantumDots.pdf

QCSE and carrier blocking in P-modulation doped InAs/InGaAs quantum dots

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