Surface passivation of InGaAs/InP HBTs using atomic layer deposited Al(2)O(3)

In this contribution, we investigate the Al2O3 surface passivation of InGaAs/InP heterostructures using thermal atomic layer deposition (ALD) with water vapor, and plasma ALD with oxygen plasma. The microstructure and optical properties of the Al2O3 layers are examined by X-ray reflectivity (XRR) and spectroscopic ellipsometry (SE) on InGaAs/InP epilayers and Si substrates. The dc current gain and breakdown voltage of InGaAs/InP heterostructure bipolar transistors (HBTs) have subsequently been used to evaluate the impact and efficiency of the ALD-Al2O3 passivation layers. The thermal-ALD-Al2O3 passivated InGaAs/InP HBTs show relatively higher current gains as compared to structures passivated using the plasma-ALD process, suggesting differences in the dielectric-semiconductor interface properties. The common emitter characteristics of both (thermal and plasma) ALD-Al2O3 passivated HBTs show, however, fairly comparable device breakdown voltages. These results will be contrasted with results from similar samples passivated with SiO2 using conventional plasma enhanced chemical vapor deposition (PECVD).