1.52 µm photoluminescence from InAs quantum dots grown on patterned GaAs buffer P. S. Wong, B. L. Liang, N. Nuntawong, L. Xue, J. Tatebayashi, S. R. J. Brueck, and D. L. Huffaker 1 Center for High Technology Materials University of New Mexico Albuquerque, NM, USA 1 Electrical Engineering Department University of California at Los Angeles Los Angeles, CA, USA huffaker@ee.ucla.edu Abstract—InAs patterned QDs (PQDs) preferentially nucleate on faceted GaAs pyramidal buffers using selective area epitaxy by metalorganic chemical vapor deposition. The photoluminescence (PL) wavelength is shown to be controlled by a single growth parameter, the growth time, without affecting the density of PQDs. Strong room temperature PL emissions over 1.5 µm from PQDs are demonstrated. The long wavelength emission is attributed to the large QD size and the partial strain energy relaxation of PQDs. Keywords-quantum dot, MOCVD, selective area growth I. INTRODUCTION Semiconductor quantum dots (QDs) have gathered much research interest due to their unique atom-like three- dimensional density of states and the subsequent huge application potential in optoelectronic industry [1-2]. In particular, GaAs based photonic devices with InAs QD emitting at the wavelength of 1.3 µm, and more importantly, 1.55 µm are very useful in fiber-optic telecommunication systems [3]. While 1.3-µm QD lasers operating at room temperature have been successfully demonstrated by several groups [4-5], GaAs based 1.55 µm QD lasers are still in pursuit. A number of approaches have been used to achieve room temperature (RT) photoluminescence (PL) peaking near 1.55 µm from InAs QDs, which include growing InAs/GaAs QDs at low temperature [6], growing on the metalorphic buffer layer [7], capping InAs QDs with InGaAs [8] or GaAsSb [9] strain-reducing layer before the GaAs capping, dilute nitride heterostructure [10], and growing large size InAs QDs [11]. In all those approaches the QDs are formed in the Stranski- Krastanow (SK) growth mode, which are characterized by random nucleation, resulting in non-uniform size and shape distributions [12]. Moreover, in the SK growth process the QD size, shape and density are strongly linked by surface kinetics as determined by growth temperature, V/III ratio and strain energy. It is difficult to independently control QD parameters like the wavelength, for example, without affecting the QD density. In this letter, we achieve RT PL emission over 1.5 µm from InAs QDs selectively nucleated on GaAs pyramidal structures grown on the nano-patterned GaAs (001) substrates. The PL wavelength is controlled by a single growth parameter, the growth time, without affecting the density of PQDs. This lithography-based approach also offers positioning flexibility for device applications. By integrating a registration mark into the lithographic process, precise registration of a single PQD or PQD ensemble with surrounding device structures can be achieved. II. EXPERIMENTS The sample growth is carried out using a low-pressure (60 torr) vertical Thomas-Swan MOCVD reactor with trimethylgallium, trimethylindium, and tertiarybutylarsine. The samples are grown on (001) GaAs substrates covered with a SiO 2 mask (25 nm thick) patterned using interferometric lithography and dry etching.[3] The patterning process results in circular openings of 230 nm (± 10 nm) in diameter with a pitch of 330 nm. The GaAs pyramidal structures are grown at 700 ˚C to form distinct equilibrium crystal shapes (ECS). The temperature is then reduced to 510 ˚C for InGaAs buffer and InAs PQD growth. The faceting of the GaAs ECS and selective InAs PQD nucleation atop are described in [4]. Two samples, Sample A and Sample B, each of size 1 cm by 1cm, are grown at the same growth conditions, except the InAs PQD growth time of Sample A, 8 seconds, is twice as long as that of Sample B. For PL analysis, the PQDs are capped with InGaAs and GaAs also at 510 ˚C. III. RESULTS AND DISCUSSION Figure 1 (c) and (d) show the HRSEM images of Sample A and B, respectively. Both Sample A and B have one single highly faceted InAs PQD nucleated on each of the {115} planes of the GaAs pyramid buffer. The PQDs of Sample A have a base dimension of 50 nm by 40 nm and a height of 20 nm, while PQDs of Sample B are smaller, with a base dimension of 40 nm by 30 nm and a height of 15 nm, due to