Electrical Characterisation of III–V Buried Heterostructure Lasers by Scanning Capacitance Microscopy

Abstract

In this work, cross-sectional scanning capacitance microscopy (SCM) is used to investigate GaAs/AlGaAs buried heterostructure (BH) lasers regrown with semi-insulating GaInP:Fe. The basic principles involved in the SCM methodology are first introduced, including resolution. The concept of doping contrast in SCM is experimentally demonstrated using InP doping staircase structure where in the doping in the different layers covers a reasonably wide dynamic range [∼10¹⁸cm⁻³ to ∼10¹⁶cm⁻³]. The capability of SCM to achieve complete electrical characterization of complex optoelectronic devices is then established using BH GaAs based lasers as an example. It is shown that a complete 2D map of the electrical properties of device structure, including delineation of regrown interfaces and the electrical nature of the regrown GaInP layer can be obtained. Characteristic peaks in the SCM signal (dC/dV) are seen at the interface between the regrown layers and the n-doped regions and attributed to band-bending at the interface. The behavior of the SCM signal with ac-bias is used to verify the semi-insulating nature of the regrown layer at different locations of the sample. The measured SCM signal for the regrown GaInP:Fe layer is uniformly zero indicating very low free carrier densities and confirms semi-insulating properties. This observation strongly suggests, in addition, uniform Fe incorporation in the regrown layers, close to and far away from the mesa. Finally, a nanoscale feature in the SCM contrast appearing as a bright spot in dC/dV mode is observed at the mesa sidewall close to the interface between the regrown GaInP:Fe and the p-barrier layer. The origin of this contrast is discussed in terms of local band-bending effects and supported by 2D Poisson simulations of the device structure.