Bias Current-voltage Characteristics Research Articles

On double exponential forward bias current-voltage (I–V) characteristics of Au/Ca3Co4Ga0.001Ox/n-Si/Au (MIS) type structures in temperature range of 80–340 K

Current transport mechanisms (CTMs) of Au/Ca3Co4Ga0.001Ox/n-Si/Au (MIS) type structures were investigated using current–voltage (I–V) characteristics in the temperature range of 80–340 K. Semilogarithmic I–V plots show two linear regions corresponding to low (0.075–0.250 V) and moderate (0.27–0.70 V) biases, respectively. Zero-bias barrier height (ΦB0) was observed to increase with increase in the temperature, whereas opposite behaviour was observed for ideality factor (n). ΦB0 and (n−1–1) vesus q/2kT and ΦB0 versus n plots were drawn to get an evidence of Gaussian distribution (GD) of the barrier heights. These plots, too, show two linear regions corresponding to low (80–160 K) and high (200–340 K) temperature ranges (LTR and HTR), respectively. Mean value of barrier height (B0) and standard deviation (σs) were extracted from the intercept and slope of ΦB0 versus q/2kT plots for two linear regions as 0.382 eV, 0.0060 V for LTR and 0.850 eV, 0.135 V for HTR at low biases and 0.364 eV, 0.0059 V for LTR and 0.806 eV, 0.132 V for HTR at high biases, respectively. B0 and Richardson constant (A*) values were also obtained from the intercept and slope of the modified Richardson (Ln(Io/T2)−(q2σs2/2k2T2) versus q/kT) plots as 131.81 Acm−2 K−2, 0.381 eV for LTR and 129.35 Acm−2 K−2, 0. 854 eV for HTR at low biases and 148.01 Acm−2 K−2, 0.377 eV for LTR and 143.77 Acm−2 K−2, 0.812 eV for HTR at high biases, respectively. In conclusion, CTM in the structure can be successfully explained in terms of thermionic emission theory with the double GD of barrier heights.

LWIR HgCdTe on Si detector performance and analysis

We have fabricated a series of 256 pixel×256 pixel, 40 µm pitch LWIR focal plane arrays (FPAs) with HgCdTe grown on (211) silicon substrates using MBE grown CdTe and CdSeTe buffer layers. The detector arrays were fabricated using Rockwell Scientific’s double layer planar heterostructure (DLPH) diode architecture. The 78 K detector and focal plane array (FPA) performance are discussed in terms of quantum efficiency (QE), diode dark current and dark current operability. The FPA dark current and the tail in the FPA dark current operability histograms are discussed in terms of the HgCdTe epitaxial layer defect density and the dislocation density of the individual diode junctions. Individual diode zero bias impedance and reverse bias current-voltage (I-V) characteristics vs. temperature are discussed in terms of the dislocation density of the epitaxial layer, and the misfit stress in the epitaxial multilayer structure, and the thermal expansion mismatch in the composite substrate. The fundamental FPA performance limitations and possible FPA performance improvements are discussed in terms of basic device physics and material properties.

A survey of CW and pulsed Gunn oscillators by computer simulation

A computer simulation survey has been carried out on X-band CW and pulsed Gunn oscillators with a variety of contact conditions. It is shown that devices with a large cathode doping notch will have a nearly constant bias voltage-frequency product for optimum RF power generation. Such a relationship is not clear for devices with a smaller notch that is large enough to cause optimum injection of dipolar space charge. For both types of device there is an optimum ratio of transit frequency and cavity controlled frequency for optimum RF power generation. Several other detailed features of operation that cannot be explained by instantaneous-domain-formation models are dealt with, including the frequency dependence of the device conductance and capacity under conditions of optimum efficiency, and the bias current-voltage characteristics.