ABSORPTION AND EMISSION SPECTROSCOPY OF SELF-ASSEMBLED INAS/GAAS QUANTUM DOTS S R Parnell, P Fry, J J Finley, D J Mowbray and M S Skolnick Department of Physics, University of Sheffield, Sheffield S3 7RH, UK. M Hopkinson, G Hill and J Clark EPSRC Central Facility for III-V Semiconductors, Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield, S1 3JD, UK. M Al-Khafaji Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield S1 3JD, UK Abstract Absorption and emission processes are studied in self-organised InAs/GaAs quantum dots using the spectroscopic techniques of photocurrent (PC) and electroluminescence (EL). Two types of dots are studied, grown using different deposition rates. Clear evidence for state filling and saturation is observed in EL spectra recorded as a function of injection current. The dependence of the transition intensities on current is found to be well described by a recently proposed model. Magneto-optical measurements in fields up to 14T provide information on the nature of the optical transitions, the spatial extent of wavefunctions and allow the determination of effective masses. I. Introduction Self-assembled InAs/GaAs quantum dots have been the subject of considerable recent interest. However many of their properties are still poorly understood, including the nature of the optical transitions, the symmetries and degeneracies of the underlying electronic states, the importance of many carrier processes and the nature of the carrier relaxation mechanisms. In this paper we employ electroluminescence (EL) and photocurrent (PC) measurements to study the optical properties of self-assembled InAs/GaAs quantum dots. We find that, unlike photoluminescence (PL), EL allows the easy filling of excited states and permits an accurate estimation of the number of injected carriers for comparison with theory. In addition, unlike PL where the Gaussian shape of the laser beam results in a spatially non- uniform carrier density. The only limitation of EL is heating effects at high currents, this can be minimised by using pulsed current injection. PC measurements allow the quantum dot absorption spectra to be measured and in contrast to photoluminescence excitation (PLE) 1 the spectra are not distorted by features arising from carrier relaxation effects. Hence PC allows the single particle electronic structure of the quantum dots to be determined. In addition a comparison of PC (dot carrier occupancy ~1) with high current EL (dot carrier occupancy >>1) allows the importance of many carrier interactions to be determined. II. Experimental Details The two InAs/GaAs self-assembled quantum dot samples studied in this work were grown at ≈500°C using conventional MBE techniques. Sample one was grown at 0.398ML/second and sample two at 0.01ML/second, both were then overgrown with a GaAs capping layer. Both samples are of the form of a GaAs p-i-n structure with a single layer of dots grown in the intrinsic