Resonant Tunnelling through InAs Quantum Dots in Tilted Magnetic Fields: Experimental Determination of the g-factor Anisotropy

We have determined the Landé factor g∗ in self-organized InAs quantum dots using resonant-tunnelling experiments. With the magnetic field applied parallel to the growth direction z we find g∗ ‖ = 0.75 for the specific dot investigated. When the magnetic field is tilted away by θ from the growth axis, g∗ gradually increases up to a value g∗ ⊥ = 0.92 when B ⊥ z. Its angular dependence is found to follow the phenomenological behaviour g∗(θ) = √ (g∗ ‖ cosθ) + (g∗ ⊥ sinθ). Introduction Resonant tunnelling experiments through zero-dimensional structures are an efficient tool to access their quantized energy levels. In recent years several groups succeeded in performing such experiments with self-assembled InAs quantum dots (QDs) embedded in the barrier of a single-barrier tunnelling device [1, 2]. Low-temperature experiments allowed to measure directly the Landé factor g of InAs dots [3, 4]. In this Note we will report on resonant tunnelling experiments through InAs QDs in tilted magnetic fields. We will show that g depends on the orientation of the magnetic field with respect to the growth direction and can be described phenomenologically by a tensor with two independent components. Sample structure The samples were grown by molecular-beam epitaxy on a highly Sidoped GaAs substrate with a donor concentration n = 2 × 10 cm. First we grew a 1-μm thick GaAs buffer layer with the same doping level followed by two 10-nm thick ndoped GaAs layers with n = 1 × 10 cm and n = 1 × 10 cm and an 15-nm thick undoped GaAs spacer. On this bottom electrode a 10-nm thick AlAs barrier was deposed. The growth of the barrier was interrupted at a thickness of 5 nm where 1.8 mono-layers of InAs were embedded in the barrier. With such an InAs coverage self-assembled InAs QDs are formed. The structure was terminated with a top electrode symmetric to the bottom electrode finishing with 1 μm highly n-doped GaAs ( n = 2× 10 cm). As a consequence of the high doping three-dimensional electrodes are present on both sides of the AlAs barrier. Subsequent to the growth of the wafer macroscopic AuGeNi contacts with a typical diameter of 50 μm were annealed into the top electrode and vertical tunnelling diodes with the same diameter were processed using wet-chemical etching. Resonant Tunnelling and Spin Splitting When a bias voltage is applied between the top and the bottom electrode our devices show I-V -characteristics which can be described by tunnelling through a single AlAs barrier [2]. Superimposed on this coarse I-V -curve physica status solidi – 2 – Rapid Research Note