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PM nanomapping of subsurface electronic and electro-mechanical properties of compound semiconductor devices - modelling vs experiment

Research output: Contribution to conference - Without ISBN/ISSN Abstract

Publication date9/07/2021
<mark>Original language</mark>English
EventMicroscience microscopy congress 2021 - Virtual event
Duration: 6/07/20219/07/2021


ConferenceMicroscience microscopy congress 2021
Abbreviated titlemmc2021
Internet address


We report a combination of an advanced sample preparation approach that uses Ar-ion nano-cross-sectioning directly suitable for the subsequent SPM imaging aiming to reveal the internal structure of advanced compound semiconductor optoelectronic devices such as vertical cavity emitting lasers (VCSELs) and GaN high efficiency light emitting nanowires. We use beam exit cross-section polishing (BEXP) that creates an oblique section with sub-nm surface roughness through the whole VCSEL structure. We then use three different SPM measurement modes – nanomechanical local elastic moduli mapping via Ultrasonic Force Microscopy (UFM), surface potential mapping via Kelvin Probe Force Microscopy (KPFM) and mapping of local piezoelectric properties via Piezoforce Microscopy (PFM). This approach revealed the 3D structure of the whole VCSEL device (Fig.1), including active cavity multiple quantum wells (MQW), obtaining profiles of differential doping of the DBR stack, and profile of electric potential in the active cavity. By applying forward bias to the VCSEL to initiate laser emission, we were able to observe distribution of the potential in the working regime, paving the way to understanding the 3D current flow in the complete device. In order to observe 3D structure of more complex structures - such as Gallium Nitride (GaN) nanowires (NWs), which geometry is ideal for the two-dimensional confinement of electrons, holes and photons for LED, photodetectors and telecommunications systems, we used the coating by Spin On Glass (SOG) before the BEXP sectioning (Fig.2). The PFM of the sections revealed that each NW can consist of several domains, with directional (vertical and shear) PFM allowing to characterize the orientation of these as in Fig 2 c-d). In order quantify the 3D SPM data, we used finite element modelling (FEM) that confirmed the experimental results of the measurements of the local doping profiles and charge distribution in the active area of the VCSEL around the oxide current confinement aperture, and allowed to interpret the orientation of the internal domains in the iii-v NWs. The novel approach not only allows to reveal currently inaccessible hidden properties of complex semiconductor nanostructures but also to quantify those providing a vital tool for the researchers and engineers developing new unique semiconductor and optoelectronic devices.