J. K. White

Two-dimensional profiling of carriers in a buried heterostructure multi-quantum-well laser: Calibrated scanning spreading resistance microscopy and scanning capacitance microscopy

We report results of a scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM) study of the distribution of charge carriers inside multi-quantum-well (MQW) buried heterostructure (BH) lasers. We demonstrate that individual quantum-well–barrier layers can be resolved using high-resolution SSRM. Calibrated SSRM and SCM measurements were performed on the MQW BH laser structure, by utilizing known InP dopant staircase samples to calibrate the instrumentation. Doping concentrations derived from SSRM and SCM measurements were compared with the nominal values of both p- and n-doped regions in the MQW BH lasers. For n-type materials, the accuracy was bias dependent with SSRM, while for SCM, excellent quantitative agreement between measured and nominal dopant values was obtained. The SSRM was able to measure the dopant concentration in the p-type materials with ∼30% accuracy, but quantitative measurements could not be obtained with the SCM. Our results demonstrate the utility of c...

Direct imaging of the depletion region of an InP p-n junction under bias using scanning voltage microscopy

We directly image an InP p–n junction depletion region under both forward and reverse bias using scanning voltage microscopy (SVM), a scanning probe microscopy (SPM) technique. The SVM results are compared to those obtained with scanning spreading resistance microscopy (SSRM) measurements under zero bias on the same sample. The SVM and SSRM data are shown to agree with the results of semiclassical calculations. The physical basis of the SVM measurement process is also discussed, and we show that the measured voltage is determined by the changes in the electrostatic potential and the carrier concentration at the SVM tip with and without the applied bias.

Electrical Scanning Probe Microscopy: Investigating the Inner Workings of Electronic and Optoelectronic Devices

Semiconductor electronic and optoelectronic devices such as transistors, lasers, modulators, and detectors are critical to the contemporary computing and communications infrastructure. These devices have been optimized for efficiency in power consumption and speed of response. There are gaps in the detailed understanding of the internal operation of these devices. Experimental electrical and optical methods have allowed comprehensive elaboration of input–output characteristics, but do not give spatially resolved information about currents, carriers, and potentials on the nanometer scale relevant to quantum heterostructure device operation. In response, electrical scanning probe techniques have been developed and deployed to observe experimentally, with nanometric spatial resolution, two-dimensional profiles of the electrical resistance, capacitance, potential, and free carrier distribution, within actively driven devices. Experimental configurations for the most prevalent electrical probing techniques based on atomic force microscopy are illustrated with considerations for practical implementation. Interpretation of the measured quantities are presented and calibrated, demonstrating that internal quantities of device operation can be uncovered. Several application areas are examined: spreading resistance and capacitance characterization of free carriers in III-V device structures; acquisition of electric potential and field distributions of semiconductor lasers, nanocrystals, and thin films; scanning voltage analysis on diode lasers—the direct observation of the internal manifestations of current blocking breakdown in a buried heterostructure laser, the effect of current spreading inside actively biased ridge waveguide lasers, anomalously high series resistance encountered in ridge lasers—as well as in CMOS transistors; and free-carrier measurement of working lasers with scanning differential spreading techniques. Applications to emerging fields of nanotechnology and nanoelectronics are suggested.

Two-dimensional transverse cross-section nanopotentiometry of actively driven buried-heterostructure multiple-quantum-well lasers

We report results of two-dimensional local potential measurement of the transverse cross-section of operating buried-heterostructure (BH) multiple-quantum-well lasers. The measured two-dimensional image of potential distribution resolved clearly the multiquantum-well active region and the p-n-p-n current-blocking structure of the BH laser, showing close correlation to the scanning spreading resistance microscopy image. Nanopotentiometry measurements were also performed on the p-n-p-n current-blocking structure of a BH laser under different forward bias voltages. The nanopotentiometry results provide direct insight into the behavior of p-n-p-n current-blocking layers intended to minimize current leakage. Our results demonstrate the application of nanopotentiometry to the delineation of complex buried structures in quantum optoelectronic devices.

Direct observation of lateral current spreading in ridge waveguide lasers using scanning voltage microscopy

We report results of two-dimensional (2D) local voltage measurement of the transverse cross section of operating multiquantum-well ridge-waveguide (RWG) lasers. We observe lateral nonuniformity of local voltage in the n-cladding layers of the laser and attribute the voltage variation to 2D carrier transport effect within the RWG lasers. The quantitative evaluation of this effect indicates the local vertical current density to be ∼40% smaller at the edge of the ridge than at its center. Our results demonstrate the strength and application of scanning voltage microscopy technique in quantitatively delineating 2D current flow in operating optoelectronic devices.

Scanning voltage microscopy on buried heterostructure multiquantum-well lasers: identification of a diode current leakage path

We report scanning voltage microscopy (SVM) results on actively driven buried heterostructure (BH) multiquantum-well (MQW) lasers that exhibit current blocking failure at high current injection operation. The measured two-dimensional image of local voltage distribution delineates the buried structures of the BH laser. The results, in combination with light-current-voltage (L-I-V) measurements, connect macroscopic external performance to measurements on the nanometer scale. Our experimental results suggest that the current blocking breakdown observed in the MQW BH lasers correlates with the turn-on of a diode leakage path when the devices are biased at high current injection.

Scanning voltage microscopy on active semiconductor lasers: the impact of doping profile near an epitaxial growth interface on series resistance

We apply scanning voltage microscopy to actively biased multiquantum-well ridge-waveguide semiconductor lasers. We localize the source of a major and hitherto unexplained sample-to-sample difference in current-voltage characteristics to the responsible junction. This is found to correspond to the regrowth interface, subsequently confirmed through secondary ion mass spectrometry to have different doping profiles in the two cases. By comparing the internal voltage profile of the operating lasers, we found that a voltage difference of 0.44 V occurred within /spl sim/100 nm of the regrowth interface in these laser structures, accounting for 88% of the difference in the measured series resistance. Additionally, 75% of the total device series resistance is associated with the structures heterobarriers. These results relate nanoscopic measurements to macroscopic performance and are of significance in improving device understanding, design, and reliability.

Nanoscopic electric potential probing: Influence of probe–sample interface on spatial resolution

Electric potential probing on the nanometer scale elucidates the operation of actively driven conducting, semiconducting, insulating and semi-insulating devices and systems. Spatial resolution of this analysis technique is shown to depend on the time required for the voltage measurement circuit to reach steady state with the local electric potential of the sample. Scanning voltage microscopy on actively biased buried heterostructure lasers reveals this time to be intrinsically long (10−2u2009s to 1 s) and to depend on material doping type (n- or p-type) and scan direction (to increasing or decreasing sample potential). The bandstructure of the probe–sample interface is examined and is shown to provide high incremental contact resistance to an equivalent circuit model of the measurement circuit. Practical scan speed limits are defined for accurate scanning electric potential measurements given a desired spatial resolution.

In situ resistance measurement of the p-type contact in InP–InGaAsP coolerless ridge waveguide lasers

Scanning voltage microscopy (SVM) is employed to measure the voltage division—and resulting contact resistance and power loss—at the p‐In0.53Ga0.47As–p‐InP heterojunction in a working InP–InGaAsP laser diode. This heterojunction is observed to dissipate ∼35% of the total power applied to the laser over the operating bias range. This in situ experimental study of the parasitic voltage division (and resulting power loss and series contact resistance) highlights the need for a good p-type contact strategy. SVM technique provides a direct, fast and in situ measurement of specific contact resistance, an important device parameter.

Calibrated scanning spreading resistance microscope (SSRM) on buried-heterostructure multiple-quantum-well lasers: probing individual quantum wells and free carrier concentrations

Summary form only given. We report the results of calibrated high-spatial-resolution SSRM measurement, showing that we are able to resolve individual quantum wells and determine the activated doping of the p-n-p-n thyristor current blocking layers of a BH MQW laser.