GaAsBi GaAs MQW diodes were grown Nomarski images of the

Fig. 2. Nomarski images of a) QW40 and b) QW54.Figure optionsDownload full-size imageDownload as PowerPoint slide
3.2. XRD
Initial (004) XRD scans of the diodes are shown in Fig. 3. The presence of clear superlattice (SL) peaks indicates that MQW regions of well-defined periodicity were formed. There is a significant broadening of the SL peaks for QW54 and QW63, which is often an indication of strain relaxation [14]. As only the symmetrical 004 scan was performed on these diodes, only the MQW BX-795 and average Bi content have been extracted from this data, assuming no strain relaxation. By assuming 8 nm wells of uniform Bi content, the measured MQW period and average Bi content were used to calculate the average strain in the MQW region. The predicted average strain was calculated using the nominal well and barrier thicknesses. The predicted average strain most accurately matched the measured average strain when the Bi content was set to be 2.83%.
Fig. 3. Data from the initial XRD characterization of the diodes. a) (004) ω–2θ scans of each diode, the y-axis is on a log scale and the scans have been vertically offset for clarity and b) the average strain in each MQW region measured by XRD, plotted against the estimated average strain in each MQW region assuming 8 nm wells of 2.83% Bi. The calculations were performed using the method of Ref. [13]. The error bars were estimated from the range of Bi contents negative feedback loop produced a reasonable fit between the measured and modelled XRD scans.Figure optionsDownload full-size imageDownload as PowerPoint slide