Study Of InAs Quantum-dot Materials And Devices Grown By GSMBE

Semiconductor quantum dots are important for basic physics studies and innovative optoelectronic device applications due to their discrete energy levels like single atom.Study of quantum-dot material growth and device applications has been one of the greatest interests for worldwide research groups.Thanks to the invention and development of MBE technology, self-assembled quantum dots can be formed in the Stranski-krastanov growth mode efficiently and conveniently.But it is difficult to control the growth of quantum dots due to the nature of S-K growth mode.In this thesis,high quality GaAs-based InAs self-organized QD samples were grown by gas-source molecular beam epitaxy(GSMBE).The dependence of optical properties of these QDs on InAs growth temperature,InAs layer thickness and growth temperature of capping layers were systematically revealed by atomic force microscopy(AFM)and photoluminescence (PL).Based on the optimized growth conditions,ridge-waveguide quantum-dot lasers were grown and fabricated.The lasing spectra,power and temperature characteristics of these devices are measured and analyzed.Results are summarized as follows:1.The dependence of optical property on InAs growth temperature were systematically investigated.It is found that the temperature for InAs/GaAs QDs growth in GSMBE can be divided to two zones,low-temperature zone around 425℃and high-temperature zone around 500℃respectively.PL spectra reflects that at low temperature QDs are grown with high uniformity, single-mode size distribution and excellent optical properties,and at high temperature QDs are grown with non-uniformity,multimode size distribution.The dependence on thickness of InAs deposited were studied at two temperature zones,respectively.It is found that the optimized InAs thickness at 425℃is 1.8MLs,while at 500℃samples with good optical properties can be obtained for a wide range(2.2～3.5MLs)of InAs thickness.2.The capping process were studied at different temperatures in GSMBE.It is found that,in contrast to the drastic leveling during capping in solid-source MBE,the InAs QDs exhibits excellent stability while capping in GSMBE,especially QDs grown at lower temperature.The stability of QDs grown by GSMBE may be attributed to Hydrogen passivation introduced by AsH₃.3.Ridge-waveguide quantum-dot lasers with five layers of InAs quantum dots in the active region were grown and fabricated.The laser devices are fabricated with 6μm-width ridge and different cavity lengths from 1.0mm to 2.0mm.These devices can all operate in continuous-wave mode up to the temperature of 70℃.At 20℃the lasing wavelength range is from 1.04μm to 1.08μm.Threshold current of the 6μm-width,1.5mm-cavity-length laser is 77mA,and its maximum output power is 51.5mW at 20℃(single facet)without coating. Between 20℃and 70℃the characteristic temperature of the device is 41.5K.The lasing spectra consists of several groups of multiple longitudinal modes.As injection current increases,the number of groups increases.We believe this different feature of emission spectra from that of conventional QW lasers results from non-uniformity and non-interactivity of quantum dots in the laser active region.The quantum-dot laser behaves as a collection of independent lasers.