IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 55, NO. 6, JUNE 2008 1529 Localized Electric Field Mapping in Planar Semiconductor Structures Pavlos Andrikopoulos, Thomas D. Boone, Jr., Member, IEEE, and Nancy M. Haegel Abstract—A technique for imaging the 2-D transport of free charge in semiconductor structures is used to directly map elec- tric field distributions in operating devices. Transport imaging is demonstrated in a scanning electron microscope operating in spot mode, using an optical microscope and a high-sensitivity charge-coupled detector to collect resulting luminescence from minority carrier recombination. The field is determined from the ratio of peak intensities in luminescence images with and without an applied electric field. The technique maps the intensity and direction of the electric field with high resolution. Fields are measured for both parallel plate and nonuniform current flow geometries. The results not only show excellent overall agreement with finite-element electrostatics modeling but also demonstrate the ability of the technique to measure the actual profiles that reflect local material variations and contact-related phenomena. Index Terms—Electric field distribution, localized field map- ping, near-contact electric field profiling, transport imaging. I. INTRODUCTION T HE ABILITY to make highly localized measurements of transport parameters is critical for the development of new devices and structures, particularly as the sizes of even larger scale devices, such as photon detectors and emitters and other sensors, continue to shrink. Localized measurements are of particular importance in areas, such as the near-contact region, where nonuniform behavior may be expected. A single transport measurement, like current–voltage (I –V ) profiling, will average over a range of potentially highly varying local behaviors, including contact resistance effects, material varia- tions, defects, and localized geometry considerations. Electric field measurements are particularly interesting be- cause a field, unlike resistance or capacitance, is not easily measured in a point-by-point fashion. The electric field can vary significantly due to the presence of contacts or other boundary features, defect states, near-contact space charge, or radiation damage, making the actual field profile much more complex than idealized simulations might suggest. In addition, dimensionally confined regions and transition regions are of Manuscript received November 1, 2007. This work was supported by the NSF under Grant DMR-0203397 and Grant DMR-0526330. The review of this brief was arranged by Editor H. S. Momose. P. Andrikopoulos is with Hellenic Army General Staff/Artillery Directorate, 15500 Athens, Greece (e-mail: pandrik@otenet.gr; dpb@army.gr). T. D. Boone, Jr., is with Hitachi Global Storage Technologies, San Jose, CA 95135 USA. N. M. Haegel is with the Department of Physics, Naval Postgraduate School, Monterey, CA 93943 USA (e-mail: nmhaegel@ nps.edu). Digital Object Identifier 10.1109/TED.2008.920971 increasing importance as contact technologies are developed for novel devices, such as nanowires, that require integration over a range of scales [1]. Other techniques for localized field mapping include elec- troabsorption [2], voltage contrast techniques [3], and related time-of-flight measurements to determine a localized drift ve- locity [4]. Electroabsorption has been applied, for example, to measure electric field variations in the near-contact region of proton-implanted transverse-field photorefractive quantum wells [5]. In electroabsorption, however, the direction of the field (vector nature) is not observed, and in many of the related techniques, a quantitative measurement of the field requires significant additional information or assumptions. Results can also be affected by other surface contrast effects. Interest in high-power photoconductive semiconductor switches in the 1990s led to the application of electrooptic sampling to obtain electric field images. Experiments were performed by using proximate LiTaO 3 crystals for external birefringent imaging [6] as well experiments using the elec- trooptic effect of the GaAs device itself [7]. These techniques were particularly useful for the measurement of time-dependent effects. However, spatial resolution was limited (3–5 µm), and the techniques are not easily applied to a wide range of materials. Finally, sophisticated finite-element tools exist for the sim- ulation of field profiles, but these can only serve as a guide to the actual profile in a specific structure, particularly when defects, damage, or material variations play a role. Additional techniques that can provide both magnitude and direction of the local field, with the potential for higher spatial resolution and ease of application, can complement existing approaches. The approach presented here requires minimal sample preparation, is not limited to high field applications, and has the potential to be applied nondestructively for full wafer characterization. In this brief, we describe a scanning-electron-microscope (SEM)-based technique for the local measurement of electric field. Both the magnitude and the direction of the field can be determined from a single pair of optical images, obtained through the integration of the SEM with an optical microscope and high-sensitivity camera. The approach can be applied to any material with a luminescent signature. It relies upon the locally measured variation in luminescent intensity and distribution in response to electron beam excitation under an applied field. The approach will be illustrated with control parallel plate structures and then applied to the measurement of a nonuniform cur- rent flow region in a modulation-doped AlGaAs/GaAs/AlGaAs heterostructure. 0018-9383/$25.00 © 2008 IEEE