1 Super-Broadly Wavelength-Tunable Semiconductor Nanowire Lasers on a Single Substrate A.L. Pan 1 , W.C. Zhou 1,2 , E.S.P. Leong 1 , R.B. Liu 1 , Alan C. H. Chin 1 , B.S. Zou 2 and C. Z. Ning 1 , 3 1 Department of Electrical Engineering and Center for Nanophotonics, Arizona Institute of NanoElectronics, Arizona State University, Tempe, AZ 85287 2 Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education and Micro-Nanotechnology Research Center, Hunan University, Changsha, 410082, China OCIS codes: (140.5960) Semiconductor lasers; (160.4236) Nanomaterials; (160.6000) Semiconductor materials 1. Introduction Widely tunable semiconductor lasers have many applications from spectroscopy to telecommunications. But producing lasers with large wavelength-tunability is fundamentally difficult in a conventional semiconductor laser due to the limited gain bandwidth for a fixed bandgap and due to lattice mismatch to grow materials with significantly different bandgaps. A tunable laser with tuning range larger than the gain bandwidth requires growing alloy semiconductors with tunable compositions. Unfortunately, the very limited lattice-constant mismatch required for growing high quality wafers has been the main obstacle of making semiconductor-based optoelectronic devices (such as lasers, detectors, and solar cells) with widely variable operating wavelengths. With the advent of nanowire- based technology, such restrictions can be removed when growing nanowires on an amorphous substrate or can be very much relaxed when growing on single crystal substrates. In this paper, we demonstrate a unique capability of growing alloy semiconductor nanowires of CdS x Se 1-x in the full composition range from x=0 to x=1 on a single substrate of ~ 1.2 cm in length. Our results demonstrate that CdSSe alloy nanowires of very high aspect ratio can be grown with composition grading along the substrate length direction, so that the complete alloy composition between the two binaries is covered in a substrate of ~1.2 cm in length. More importantly, we demonstrate that such nanowires on their native substrate can function as spatially wavelength-tunable lasers at high optical pumping, providing the first example of a continuously tunable laser with an unprecedented tuning range of over 200 nm. Such broadly tunable lasers may find use in many applications such as novel optical interconnects or multiplexing, multi-agent chemical or biological detections, and spectroscopy. 2. Experimental Results Our nanowires were grown on a glass substrate using the vapor-liquid-solid [1,2] method in a horizontal tube reactor with gold as catalyst. A carefully engineered temperature gradient was achieved along the length of the substrate. Since the composition of ternary semiconductor alloy nanowires depends on the local growth temperature on the substrate, such temperature gradient leads to a spatial grading of alloy composition. Various structural characterizations showed that the entire substrate is covered with high-quality alloy nanowires, with their composition changing from CdS at one end to CdSe at the other end continuously over the entire composition range of the ternary alloy. The typical wire diameters are 100-200 nm in length and tens of microns in length, randomly oriented on a substrate of 1.2 cm in length. Such nanowires are capable of lasing individually because each of them 3 Corresponding author: CZN: cning@asu.edu Abstract: We demonstrate lasing from semiconductor nanowires with wavelength continuously tunable from 500 to 700 nm on single substrate. This widest ever tuning range of any semiconductor lasers is achieved through spatial composition-grading of alloy semiconductors. a1014_1.pdf a1014_1.pdf CTuY7.pdf © 2009 OSA/CLEO/IQEC 2009 CTuY7.pdf