Characteristics of InGaAs quantum dots grown on tensile-strained GaAs/sub 1-x/P/sub x/

Abstract

The use of low-dimensional quantum dot (QD) active regions hold potential for realizing extremely low threshold current density lasers which are temperature insensitive l (i.e. high To, Tl)' Both of these factors are important for achieving high total power conversion efficiency, IIp, in diode lasers. Unfortunately, these unique features of the QD active layer have not been fully realized to date. Recently, experimental studies 2 . 3 have identified carrier leakage out of the QD as an underlying cause for low modal gain and high temperature sensitivity. Carriers which are thermally excited into the wetting layers surrounding the QD, lead to gain saturation at values significantly lower (-a factor of 4) than achievable if saturation occurs due to population inversion in the dot states.As a result, many stacked layers of QD material are needed to achieve typical threshold gain requirements in diode lasers. In addition, this carrier leakage process is highly sensitive to temperature. Recently, the use of a higher bandgap matrix4-6 imbedding the QD has been investigated, which may improve carrier confinement in the QD, and result in higher peak gain.QD lasers in the l.0/lm wavelength region have been reported using MOCVD growth, with performance comparable to MBE grown structures7• Much work to date has focused on wavelength extension towards 1.3 /lm using an InxGal_xAs compressively strained matrixR• Little work has been reported on shorter wavelength (A.,< 1 /lm) lasers grown by MOCVD. The use of a tensile-strained GaAsP or GaP matrix provides strain compensation for the compressively strained QDs and improves stacked structures9•1 O • In addition, the larger bandgap of GaAsP compared with GaAs or InGaAs should improve QD carrier confinement and allow wavelength tuning towards shorter wavelengths (i.e. 980nm), without introducing AI-containing compounds within the active region. Here, we report on the optical and structural properties of Ino.5Gao.5As (nominal composition) QDs grown on GaAs l _xP x for x=O-OAS. We find the QD ground state emission wavelength can be varied over a span of 100nm by adjusting the P content of the barrier layer. Thus, these structures have potential for achieving high performance laser structures in the shorter wavelength (A.,<l/lm) wavelength region.The InGaAs QD structures studied here (see Fig. I.) are grown by low-pressure (SOmbar) MOCVD using TMGa, TMIn, AsH" and PH 3 for group III and group V sources. The Ino.sGao.sAs QD on GaAs(P) growth temperature, growth rate and VIIII ratio were 480°C, 104 Als, and SO respectively. The thickness of the Ino.5Gao.5Aswas kept constant, 1 nm, for all structures. The growth was interrupted 60 seconds after the QD growth. During the interruption, the AsH3 was switched off to allow QD fonnation. After QD formation, a 30 A GaAs(P) cover layer was grown at same growth temperature. Subsequently, we continued to grow GaAs and AIGaAs layers at S80°C- 620°C.Variable temperature photoluminescence (PL) and atomic force microscopy (AFM) are used to characteri...

Temperature sensitivity of InGaAs quantum-dot lasers grown by MOCVD

“…Each QD layer is grown on GaAsP and covered by GaAsP and the TMIn/total group III flow ratio was 0.6 for the InGaAs QD growth, corresponding to a solid phase In composition of approximately 35%. Detailed growth conditions for the QD and barrier materials were reported previously [8]. For the threeand five-stack QD structures, a 50-nm GaAs separation layer was grown which is enough distance to uncouple of the strain of the QD layers [9].…”