InGaN Quantum Dots Fabricated on AlGaN Surfaces-Growth Mechanism and Optical Properties-
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enhanced excitonic effects which is believed to make the realization of low- threshold laser diodes possible [5]. Drastical optical gain enhancement using a biexciton- related emission is theoretically predicted and expected even at room temperature, due to the large binding energy of the biexciton in GaN- related quantum dot (QD) structures [6]. It was speculated that the emission of Nichia's InGaN- based quantum well lasers originated from dot- like states formed by nanoscale In segregated (In- rich) regions [7], thus realizing a device similar to a quantum dot (QD) laser [8]. Even though indium rich areas indeed form in thin InxGal-x N quantum wells, the observed localization behavior may, alternatively, arise from a recombination involving a defect state. Later investigations on similar diodes, including temperature- [9] and pressuredependence [10] could not provide final evidences for which mechanism that is causing the observed localization effect. The exciton localization in InxGal-x N comprising an unusually long decay time at low temperatures, first observed by Harris et. al. [11], is a well-known effect caused by alloy fluctuations [12], as pointed out by the authors. However, in order to realize QD- based devices, operating at room temperature, a stronger confinement than that created by alloy fluctuations may be required. We already succeed in the fabrication of self- assembling GaN QDs on AlGaN surfaces using metal- organic chemical vapor deposition (MOCVD) [13]. The QDs were fabricated by a growth mode change from step flow to 3- dimensional island formation modifying the surface properties with the deposition of anti-surfactant silicon on AlGaN surfaces. We have also demonstrated the stimulated emission from the GaN QDs sandwiched with separate confinement heterostructure (SCH) by optical pumping [14]. 737 Mat. Res. Soc. Symp. Proc. Vol. 482 01998 Materials Research Society
In this letter we report on the first successful fabrication of self- assembled InGaN QDs grown by MOCVD on an AlGaN surface. We will demonstrate photoluminescence (PL) from fabricated InGaN QDs from cryogenic temperatures up to above room temperature. The amount of indium incorporated in the QDs will be shown to depend strongly on the growth temperature. In addition, from the temperature- dependent energy shift of the photoluminescence peak, the localization effect in InGaN QDs will be discussed. EXPERIMENT The structures were grown, at 76 Torr on the Si- face of an on- axis 6H- SiC (0001) substrate, by a conventional horizontal- type MOVPE. As precursors ammonia (NH3), tetraethylsilane (TESi), trimethylaluminum (TMA), and trimethylgallium (TMG) were used with H2 or N2 as carrier gas. Because of the larger indium incorporation ratio compared with H2, the trimethylindiumdi- i- propyalamine adduct ((CH3)3)In(i-C 3H7)2NH was supplied with N2 as carrier gas. N2 gas was also independently supplied by a separate line and mixed with the H2 just before the substrate susceptor. Typical gas flows were 2 standard (at 760 Torr) liters per
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