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. . In a comment 1 on our recent letter, 2 Yu first pointed out that there was strong alloying between the Ge dots and barrier layers because of the appearance of Si–Ge mod also observed in SiGe alloys. It is correct that the Ge samples reported in our letter have some degrees of allo due to interdiffusion. This was due to the fact that t samples were grown at a high temperature of 600 °C. reason for using this temperature came from our intention control the size uniformity. It was found that an optimu temperature occurs at around 600 °C for high-uniform mo modal Ge dots on planar Si substrate. 3,4 At lower temperatures, the uniformity becomes worse. Moreover, two kinds dots coexisted on the Si substrate ~pyramid and dome !. Figure 1~a! shows a cross-sectional TEM image of a te period Ge quantum dot sample grown at 550 °C ~sample 1!. Vertically correlated dots are evident. The size variation the first Ge dot layer, however, is determined to be 20% fr AFM measurements@Fig. 1~b!#. The nonuniformity arises from limited diffusion at the lower growth temperature 5 and becomes worse in the vertically correlated multilayers cause vertical correlation rearranges the strain distribut leading to the fact that the upperlayer dots are larger t those in the lower layers @Fig. 1~a!#. On the other hand, at higher temperature around 600 °C, the dot uniformity much improved and the size variation decreases to, for ample 7%–8% in our samples in the letter. 2 Such uniformity may be desirable, but the interdiffusion between the Ge d and Si spacers reduces quantum confinement effects a undesirable for optical applications. Thus, there is alway tradeoff between the uniformity and interdiffusion. Now let us take a look at the Raman spectrum of sample 1@Fig. 1~c!#. This figure includes a spectrum for ten-period Ge dot superlattice grown at 500 °C ~sample 2!. One can easily see Si–Ge vibration modes at around cm from both samples. The relative strength I Si–Ge/I Ge–Ge decreases as the temperature decreases. Another phe enon is that there is a weak feature ~indicated by an arrow in the figure! between Si–Ge mode and Si–Si mode for sam 1. This is due to localized Si–Si motion in the neighborho of one or more Ge atoms. 6 Such kinds of localized Si–S optical modes~Si–Siloc! are often observed in SiGe alloy

applied physics letters

Response to “Comment on ‘Optical and acoustic phonon modes in self-organized Ge quantum dot superlattices’ ” [Appl. Phys. Lett. <b>78</b>, 1160 (2001)]

Response to “Comment on ‘Optical and acoustic phonon modes in self-organized Ge quantum dot superlattices’ ” [Appl. Phys. Lett. 78, 1160 (2001)]