## 4 Selective Area Growth Applied on InPSi Wafers
### Multi Wavelength Laser Array Grown on InPoSi  
Based on these MQW-based active regions obtained by SAG, five laser structures were simultaneously grown on InPoSi. The first laser was made in the field area, far from the four other pairs of selective masks, for which W\({}_{\text{m}}\) values were set to be 5 \(\upmu\)m, 15 \(\upmu\)m, 20 \(\upmu\)m and 30 \(\upmu\)m. In the field area, the grown laser structure is composed of a 500 nm thick n-doped InP contact layer, a 6 period AlGaInAs MQW-based active region, a 2 \(\upmu\)m-thick p-doped InP cladding layer and a 200 nm-thick p-doped InGaAs contact layer. Then, five shallow-ridge  
Figure 8: Morphologic characterizations of the selectively grown AlGaInAs-based MQW structures on InPoSi: (**a**) PL measurements for SAG masks’ widths ranging from 5 \(\upmu\)m to 30 \(\upmu\)m; (**b**) HRXRD profiles obtained with a micro-focus X-ray source; Cross-section TEM image obtained in SAG regions obtained with (**c**) W\({}_{\text{m}}\) = 5 \(\upmu\)m; (**d**) W\({}_{\text{m}}\) = 30 \(\upmu\)m.  
lasers were fabricated. Finally, 500 \(\upmu\)m long bars containing all the lasers were cleaved and soldered on thermally conductive submounts. A photograph and a microscopic image of the laser array are shown respectively in Figure 9a,b. A facet of one of the shallow-ridge lasers in the array was observed by SEM, as shown in Figure 9c.  
The emitted signals were coupled by a standard lensed optical fiber to an optical spectrum analyzer Anritsu MS970 and are shown in Figure 10a. Emission spectra are peaking at 1515 nm, 1580 nm, 1610 nm, 1635 nm and 1670 nm for different SAG areas. This covers a 155 nm-wide spectral band including the whole C+L band under continuous-wave operation. The L-I characteristics measured using a broad-area detector in CW operation at 20 \({}^{\circ}\)C are presented in Figure 10b. Laser threshold currents remain below 30 mA at 20 \({}^{\circ}\)C for the lasers emitting from 1515 nm up to 1610 nm. At least 17 mW of output power is achieved for 200 mA injected current for those lasers. I-V curves are shown on Figure 10c. The mean sheet resistance is of 6.6 \(\Omega\pm 1\)\(\Omega\).  
For the longest wavelengths (>1610 nm), the threshold current increased up to 60 mA at 20 \({}^{\circ}\)C. This degradation is due to the enlargement of the quantum barrier (QB) and SCH layers in the optical cavity obtained by SAG. This can be also due to the enlargement of the p-doped cladding layer. This undesirable effect could be reduced by lowering the work pressure, hence reducing SAG effect, for the growth of this specific layer. The MQW design could also be optimized for this broad spectral range in order to homogenize laser performance.  
Figure 10: Static characteristics measured for the five lasers in the array under CW operation: (**a**) emission spectra measured @20 \({}^{\circ}\)C under 100 mA driving current; (**b**) light-current characteristic measured @20 \({}^{\circ}\)C; (**c**) current-voltage characteristics measured at 20 \({}^{\circ}\)C.  
Figure 9: Selectively grown laser array on silicon: (**a**) photograph of the chip mounted on a thermally conductive submount; (**b**) Microscopic image of the laser array; (**c**) Cross-section of a shallow-ridge laser observed by SEM.  
Next, the thermal stability of the lasers was tested up to 70 \({}^{\circ}\)C under CW operation for the lasers emitting at 1515 nm, 1580 nm and 1610 nm. The results are presented in Figure 11. The lasing effect remains at least up to 70 \({}^{\circ}\)C. The laser characteristic temperature T\({}_{0}\) is 69 \({}^{\circ}\)C for the three lasers. This result demonstrates that these AlGaInAs MQW-based active regions that are selectively grown have similar thermal behavior.