JOURNALOF MATERIALS SCIENCE: MATERIALS IN ELECTRONICS 14 (2003) 357±360 Photoluminescence study of strain-induced GaInNAs/GaAs quantum dots H. KOSKENVAARA, T. HAKKARAINEN, H. LIPSANEN, M. SOPANEN Helsinki University of Technology, Optoelectronics laboratory, P.O. Box 3500, FIN-02015 HUT, Finland E-mail: hannu.koskenvaara@hut.® Strain-induced Ga 0.8 In 0.2 N y As 1  y quantum dots on GaAs were fabricated by metal organic vapor phase epitaxy. Nitrogen concentration y was varied between 0% and 1.3%. The effect of nitrogen concentration on the optical properties of the quantum dots was investigated by continuous-wave and time-resolved photoluminescence measurements. Carrier localization in the states below the band edge of the nitrogen-containing quantum well has been observed. These states are thought to originate from the variation of the quantum well width or from the ¯uctuation of the composition. Such variations have been identi®ed in GaInNAs quantum wells on GaAs without stressor islands. The measured energy difference of the quantum well and quantum dot ground-state peak energies increase with increasing temperature. # 2003 Kluwer Academic Publishers 1. Introduction In recent years, Ga x In 1  x N y As 1  y grown on a GaAs substrate has been studied intensively. The large band- gap bowing and the possibility of lattice matching with GaAs substrate make GaInNAs quantum wells and dots potentially suitable for long-wavelength (1.3 and 1.55 mm) optical communications. For example, laser diodes having improved high-temperature performance [1], vertical cavity surface emitting lasers [2] and ef®cient multi-junction solar cells [3] have been reported as applications of GaInNAs quantum wells. Recently, quantum dots of GaInNAs have been grown by molecular beam epitaxy (MBE) directly on GaAs [4]. In this work we have fabricated, by metal organic vapor phase epitaxy (MOVPE), strain-induced GaInNAs quantum dots by using InP stressor islands grown on top of the GaInNAs quantum well. The self-organized InP stressors have been used earlier in strain-induced GaInAs quantum dots on GaAs [5]. The effect of nitrogen concentration on the optical properties of the quantum dots is studied. Recent studies [6, 7] suggest that incorporation of a few per cent of nitrogen induces localized states in the band gap of the GaInNAs quantum well. Possible effects of this localization on the recombination lifetime and the energies of the quantum dot states have been investigated. 2. Experimental procedure The samples were grown on semi-insulating GaAs (1 0 0) substrates in a horizontal MOVPE reactor at atmospheric pressure. Trimethylgallium, trimethylindium, tertiarybu- tylarsine, tertiarybutylphosphine, and dimethylhydrazine were used as source materials for gallium, indium, arsenic, phosphorus, and nitrogen, respectively. A 8-nm thick Ga 0:8 In 0:2 N y As 1  y quantum well and a 5-nm thick GaAs barrier layer were grown at 530  C on a 100-nm thick GaAs buffer layer. Thermal annealing at 650  C was subsequently performed for 10 min to enhance the optical performance of the samples. After annealing, a 5- nm GaAs cap layer was grown on the barrier layer to smooth the sample surface. Then, an InP layer with a nominal thickness of three monolayers was fabricated. The growth mechanism of InP on GaAs is the coherent Stranski±Krastanow growth, which produces self-orga- nized islands with a relatively homogenous size distribution. These islands act as stressors inducing a lateral quantum dot potential in the quantum well due to tensile strain. Dimensions and lateral density of the islands have been measured by atomic force microscopy. The base diameter of the islands was about 100 nm and their height was about 20 nm. The lateral density of the islands was 1±2610 9 cm  2 . The nitrogen concentration of the quantum wells was varied from 0% to 1.3%. More details about the growth of the quantum wells can be found in Hakkarainen et al. [8]. Optical properties of the samples were studied by photoluminescence (PL) spectrometry and time-resolved photoluminescence measurements. The sample tempera- ture was controlled from 9 K to room temperature in a closed-cycle helium cryostat. In the continuous-wave PL spectrum measurements a 488-nm line from an argon ion laser was used for excitation. Luminescence was collected into a liquid-nitrogen-cooled germanium pin- detector through a 0.5-m monochromator. In the time- resolved PL measurements the sample was excited by 150-fs pulses at the wavelength of 800 nm from a mode- locked titanium-sapphire laser. Signal was detected by a 0957±4522 # 2003 Kluwer Academic Publishers 357