ELS EVI E R Thin Solid Films 380 (2000) 183-188 www.elsevier.com/locate/tsf Self-assembling InAs and InP quantum dots for optoelectronic devices K. Eberl", M. Lipinski, Y.M. Manz, N.Y. Jin-Phillipp, W. Winter, C. Lange, O.G. Schmidt Max-Planck-Insitut fur Festkorpegorschung, Heisenbergstr. 1, 70569 Stuttgart, Gemany Abstract Stranski-Krastanov growth in molecular beam epitaxy allows the preparation of self assembling InAs and InP quantum dots on GaAs and Ga0,521no,4,P buffer layers, respectively. InAs dots in GaAs prepared by slow growth rates and low temperature overgrowth provide intense photoluminescence at the technologically important wavelength of 1.3 p,m at room temperature. Strain induced vertical alignment, size modification and material interdiffusion for stacked dot layers are studied. A blue shift of the ground state transition energy is observed for the slowly deposited stacked InAs dots. This is ascribed to enhanced strain driven intermixing in vertically aligned islands. For very small densely stacked InP and InAs dots the reduced confinement shift causes a red shift of the ground state emission. The InP quantum dots show intense and narrow photoluminescence at room temperature in the visible red spectral range. First InP/Ga0,521no,4,P quantum dot injection lasers are prepared using threefold stacked InP dots. We observe lasing at room temperature in the wavelength range between 690-705 nm depending on the size of the stacked InP dots. 0 2000 Elsevier Science B.V. All rights reserved. Keywords: Self assembling dots; InAs; InP; Quantum dot laser; Stacked dots 1. Introduction A simple method to prepare semiconductor quantum dots (QD) is based on island formation in strained layer epitaxy. For example, the lattice mismatch between InAs and GaAs is approximately 7%. Deposi- tion of InAs on GaAs (100) at substrate temperatures of typically T, 450-500°C results in the formation of a 1.5-1.8 monolayer (ML) thick wetting layer. Beyond this thickness islands appear on the surface. This is known as Stranski-Krastanov growth mode. InAs 111, InP [2] and Ge [3] quantum dots that have dimensions of only a few nanometers across have been prepared this way by different research groups. demonstrated advantages are: Access to new energies, since materials with different lattice constants and en- ergy gaps can be combined, improved temperature stability and low threshold current densities (jth 1. In fact, a record low threshold current density of 19 A/cm2 was reported for InAs quantum dots lasers emitting at 1.3 pm at room temperature [5,6]. This is more than a factor of two lower than quantum well lasers [7]. Additional advantages of quantum dots are the lower sensitivity to dislocations, and the enhancement of light emission and absorption from indirect semiconductors. The latter is explained by the spread of the wave function in k-space due to strong carrier localization - - Quantum dots find significant interest especially for applications in laser diodes [4]. The expected and partly 181. 2. Preparation of Ids quantum dots * Corresponding author. E-mail address: eberl@servix.mpi-stuttgart.mpg.de (K. Eberl). The InAs/GaAs samples have been fabricated by 0040-6090/00/$ - see front matter 0 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 0 - 6 0 9 0 ( 0 0 ) 0 14 9 9 - 1