Abstract
Electron channelling contrast imaging (ECCI) performed in a scanning electron microscope (SEM) is a rapid and non-destructive structural characterisation technique for imaging, identifying and quantifying extended defects in crystalline materials. In this review, we will demonstrate the application of ECCI to the characterisation of III-nitride semiconductor thin films grown on different substrates and with different crystal orientations. We will briefly describe the history and the theory behind electron channelling and the experimental setup and conditions required to perform ECCI. We will discuss the advantages of using ECCI, especially in combination with other SEM based techniques, such as cathodoluminescence imaging. The challenges in using ECCI are also briefly discussed.
Highlights
IntroductionIII-nitrides are the only class of commercially available inorganic semiconducting materials with the potential to emit light from the infrared to the ultraviolet (with commercial devices available in the green to the ultraviolet part of the spectrum) with direct band gaps ranging from 0.7 eV for InN to 6.2 eV for AlN [1]
III-nitrides are the only class of commercially available inorganic semiconducting materials with the potential to emit light from the infrared to the ultraviolet with direct band gaps ranging from 0.7 eV for InN to 6.2 eV for AlN [1]
Electron channelling contrast imaging (ECCI) of GaN thin films In ECCI, vertical threading dislocations appear as spots with black–white (B–W) contrast; this is shown in Fig. 2a, an ECC image acquired from a 1600 nm thick GaN thin film grown on a sapphire substrate in which a typical threading dislocation is highlighted by a black circle [49]
Summary
III-nitrides are the only class of commercially available inorganic semiconducting materials with the potential to emit light from the infrared to the ultraviolet (with commercial devices available in the green to the ultraviolet part of the spectrum) with direct band gaps ranging from 0.7 eV for InN to 6.2 eV for AlN [1]. Through results from a wide range of nitride thin films grown by metalorganic vapour phase epitaxy (MOVPE), we will illustrate that ECCI can be used to reveal (i) individual dislocations, (ii) atomic steps, (iii) low angle tilt and rotation boundaries, and (iv) basal plane stacking faults and associated partial dislocations. Some of our own work [36,37,38,39,40] and recent work from our collaborators [41,42,43] have taken ECCI a step further as a quantitative technique for characterising nitride semiconductor thin films by resolving individual dislocation types over statistically significant dislocation distributions, opening up new possibilities for advanced materials characterisation
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