Light-Emitting Devices with Self-Formation Disordered Quantum Dots

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The disordered superlattices of SiGe material system were fabricated to investigate the enhancement of luminescence capability of an indirect transition semiconductors. In a disordered superlattices, individual thicknesses of layers are randomly variated. The luminescence enhancement becomes greater with increasing the composition rate x and at most 50 times in x<0.55 of Si^<1-x>Ge^x/Si. The insertion of SiGe alloy buffer layer between Si substrate and a grown layer enhances the luminescence further.The stacked (lnAs/GaAs)-layers in which the thicknesses of GaAs spacers were gradually varied were grown to find an optimum spacer thickness. It was determined by the TEM observations : between h and 2h. Here h is the the height of InAs quantum dots. Below h the dots were demolished and beyond 2h the dots were not stacked. The investigations of luminescence enhancement by the stacked layers will be entered into details.The self-formed InP quantum dots on the GaP substrate were grown in plac … More e of on the AlP substrate which is difficult to obtain. The dots are hardly formed and their sizes tend to be large : 400-500nm at a conventional growth temperature 550ﾟC.We succeeded to form the dots of 25-4Onm in size by decreasing the growth temperature to 420ﾟC.In our growth experiments, it was found that InN and GaN do not become a uniform solid solution, but InN is segregated in GaN.The segregation can be suppressed by increasing the growth temperature, but the growth rate becomes extremely low. Our plasma-excited growth method can grow a uniform InGaN at lower temperature.The segregated InN would be utilized for the quantum dot formation, provided their sizes are small enough to exhibit quantum effects. Optimum conditions for the quantum dots formation of InN are future subjects.These fundamental experimental achievements are worthwhile to actualize a high efficiency of light-emitting devices by quantum structured semiconductors. Details were published in 7 papers of scientific journal and 2 oral presentaions. Less