Threading dislocation density characterization in III–V photovoltaic materials by electron channeling contrast imaging

Abstract

Accurate and rapid threading dislocation density (TDD) characterization of III-V photovoltaic materials using electron channeling contrast imaging (ECCI) is demonstrated. TDDs measured using ECCI showed close agreement with those from electron beam-induced current mapping (EBIC) and defect selective etching (DSE). ECCI is shown to be well-suited for measuring TDD values over a range of ~ 5×10 6 to 5×10 8 cm-2. ECCI can distinguish individual dislocations in clusters closer than 0.2 µm, highlighting its excellent spatial resolution compared to DSE and EBIC. Taken together, ECCI is shown to be a versatile and complementary method to rapidly quantify TDD in III-V solar cells.

Direct Growth of a GaInP/GaAs/Si Triple‐Junction Solar Cell with 22.3% AM1.5g Efficiency

“…Material characterization was performed in a Hitachi SU-70 scanning electron microscope using the electron channeling contrast imaging (ECCI) method. [22] IV characteristics were measured in the Fraunhofer ISE CalLab using a three-zone solar simulator adjusted to 1-sun AM1.5g standard test conditions. [23] During IV measurements, an aperture mask was applied to the cells with the Si substrate to avoid any contribution of photogenerated charge carriers in the Si wafer from outside the cell area.…”

Low threading dislocation density GaAs growth on on-axis GaP/Si (001)

“…15,16 Instead, the ECCI technique has recently received much attention as a useful tool for non-destructive, rapid, and accurate TD measurement for III-V materials. [17][18][19] Furthermore, TDs generated during strain relaxation tend to form in clusters and the limited resolution (a few microns) of the EPD technique can result in underestimating the actual TDD. 15,20 A FEI Quanta 400f scanning electron microscope equipped with a fieldemission electron gun and a pole-piece mounted back-scattering detector was used for ECCI.…”

Microscopy of defects in semiconductors

“…Any deviation in crystallographic orientation or in lattice constant due to local strain, may then be revealed by variation in the contrast in the electron channelling image constructed by monitoring the intensity of backscattered or forescattered electrons as the electron beam is scanned over the sample. Extremely small changes in orientation and strain are detectable, revealing, for example, low angle tilt and rotation boundaries and atomic steps and enabling extended defects such as dislocations and stacking faults to be imaged [21,22,23,24,25,26,27,28,29]. ECCI can provide similar information on defects as the transmission electron microscope (see sections 10.2.3 and 10.3.1.4) where the defects either thread to the surface or lie within around 50 nm of the surface.…”

“…Until recently, ECCI was mostly used to investigate the structural properties of metals and geological materials, but its use for the characterisation of defects in semiconductors is steadily expanding. To date ECCI has been used to image defects in nitride semiconductors [22,23,24], Si1-xGex [34], SiC [35], GaAs [26], GaP [27,28], GaAsyP1-y [28], GaSb [29]. For more information on ECCI, the following papers provide informative reviews of the technique [21,29,34,35].…”

“…Other examples of combining luminescence information from CL with structural information from ECCI are the investigation of growth temperate of GaInP on TDs [70] , grain boundaries in CdTe thin film solar cells [129] or the investigation of recombination behaviour of dislocations in III-V photovoltaic materials using electron beam-induced (EBIC) instead of CL [130].…”