Influence of buffer-layer surface morphology on the self-organized growth of InAs on InP(001) nanostructures

We have studied the influence of InP buffer-layer morphology in the formation of InAs nanostructures grown on InP~001! substrates by solid-source molecular-beam epitaxy. Our results demonstrate that when InP buffer layers are grown by atomic-layer molecular-beam epitaxy, InAs quantum dot-like structures are formed, whereas InP buffer layers grown by MBE produce quantum-wire-like structures. The optical properties of these corrugated structures make them potential candidates for their use in light-emitting devices at 1.55 mm. © 2000 American Institute of Physics. @S0003-6951~00!00309-0# InAs nanostructures grown on InP~001! are promising candidates for light emitting devices in the wavelength range 1.3‐1.55 mm. 1‐3 A widely investigated technological approach is to use self-organized nanostructures that appear spontaneously as an efficient way to relax elastic strain in lattice-mismatched heteroepitaxy. In order to obtain a welldefined emission wavelength, nanostructures should have a good uniformity in size and shape. Ordering in the growth plane and a precise control of the nanostructure morphology is a key issue for self-organized systems. Due to a 3.2% lattice mismatch of InAs on InP~001!, elastic strain relaxation takes place above a certain critical thickness via a change of morphology from two-dimensional ~2D! to threedimensional ~3D!. Much of the research developed on selforganized growth of InAs on InP substrates is devoted to quantum-dot ~QD! formation. 1‐4 However, very recent results 5 have shown that the chemical composition of the buffer layer ~InP, InGaAs, or InAlAs! is determinant in configuring the final shape of the InAs self-organized nanostructures. In this letter, we demonstrate that the growth conditions of the InP buffer layer also controls the surface rearrangement of the strained InAs layer grown on top. Therefore, it is possible to obtain either QD or quantum-wire ~QWr! structures for identical InAs coverage and growth conditions. There are two sets of samples grown for this work. In the first one, InAs was deposited on a 200-nm-thick InP buffer layer grown either by molecular-beam epitaxy ~MBE! or by atomic-layer molecular-beam epitaxy ~ALMBE !~ Ref. 6! using solid sources. MBE buffer layers were grown in the 234 surface reconstruction at T s 5460 °C and at a beamequivalent pressure ~BEP! (P2)55310 26 Torr. For the ALMBE InP buffer layers, a substrate temperature Ts 5400 °C is used. The P 2 pulsed flux reaching the surface sample is controlled by means of the reflectivity difference ~RD! technique in order to optimize surface stoichiometry for growing InP planar surfaces. 6 The InAs layers, 2.5 ~ML! thick, were deposited at a BEP (As 4 )51.5‐ 2310 26 Torr, a growth rate of 0.5 ML/s, and Ts5400 °C, which is chosen to minimize the P/As exchange. After InAs growth, an annealing at 480 °C under arsenic pressure during 10‐20 s was performed. We observe, in agreement with other authors, 3,4 that InAs growth takes place in a 2D mode. The 2D‐3D transition occurs during the annealing process at Ts 5480 °C, as shown by a change into a spotty reflection high-energy electron diffraction ~RHEED! pattern. The second set of samples consist of 5-, 8-, and 12-ML-thick InxGa12xAs layers with In contents x50.95, 0.9, and 0.85, respectively, deposited on InP buffer layers grown by MBE. We have increased the layer thickness for decreasing x according to the expected dependence of critical thickness with misfit. 7