The electronic properties of a self-assembled GaSb/GaAs QD ensemble are determined by capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS). The charging and discharging bias regions of the QDs are determined for different temperatures. With a value of 335 (±15) meV the localization energy is rather small compared to values previously determined for the same material system. Similarly, a very small apparent capture cross section is measured ( ？cm2). DLTS signal analysis yields an equivalent to the ensemble density of states for the individual energies as well as the density function of the confinement energies of the QDs in the ensemble. 1. Introduction GaSb/GaAs quantum dots are an interesting material system due to their type-II band alignment with its exclusive hole confinement and a barrier present for electrons [1]. In particular for charge storage applications, they are a promising option due to not only the very large barriers that can be achieved [2–5] but also the spatial separation of electrons and holes which facilitates long exciton lifetimes [6, 7] and could lead to interesting long-wavelength optoelectronic applications [8]. Although growth by metal organic vapor phase epitaxy (MOCVD) has been demonstrated [9, 10], the common way to fabricate these dots is molecular beam epitaxy (MBE) due to the peculiarities of Sb (i.e., smaller vapor pressure of Sb as compared to As, Sb crystal formation). For the use of GaSb/GaAs QDs in applications knowledge of their electronic properties is required. In this paper, we present an investigation of the electronic structure of GaSb/GaAs QDs. We analyze static as well as time-resolved capacitance-voltage (C-V) measurements, in particular deep-level transient measurements (DLTS), in order to determine the key electronic properties, such as the activation energies, the localization energy, and the apparent capture cross sections of the QD ensemble. The analysis of the DLTS signal yields an equivalent to the density of states of the QD ensemble for each individual energy. 2. Sample The sample is grown by MBE. It consists of a layer of GaSb QDs embedded on the -side of a diode. The design allows to charge and discharge the QDs with holes in a controlled way. The layer structure is the following: on top of an -doped GaAs substrate a 300？nm wide highly doped ( ？cm？3) layer is grown as back contact. Then, a 500？nm wide -doped ( ？cm？3) layer is deposited, followed by 7？nm nominally undoped GaAs. On top of the undoped layer, 3 ML GaSb are deposited to form QDs with a growth interruption to prevent
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