This paper reports data for back-illuminated planar n-on-p HgCdTe electroninitiated avalanche photodiode (e-APD) 4 · 4 arrays with large unit cells (250 · 250 lm 2 ). The arrays were fabricated from p-type HgCdTe films grown by liquid phase epitaxy (LPE) on CdZnTe substrates. The arrays were bumpmounted to fanout boards and characterized in the back-illuminated mode. Gain increased exponentially with reverse bias voltage, and the gain versus bias curves were quite uniform from element to element. The maximum gain measured was 648 at -11.7 V for a cutoff wavelength of 4.06 lm at 160 K. For the same reverse-bias voltage, the gains measured at 160 K for elements with two different cutoff wavelengths (3.54 lm and 4.06 lm at 160 K) show an exponential increase with increasing cutoff wavelength, in agreement with BeckÕs empirical model for gain versus voltage and cutoff wavelength in HgCdTe e-APDs. Spot scan data show that both the V = 0 response and the gain at V = -5.0 V are spatially uniform over the large junction area. To the best of our knowledge, these are the first spot scan data for avalanche gain ever reported for HgCdTe e-APDs. Capacitance versus voltage data are consistent with an ideal abrupt junction having a donor concentration equal to the indium concentration in the LPE film.
An optical waveguide phase modulator has been fabricated on X-cut LiNbO(3) by using proton exchange in benzoic acid. The phase modulator was operated as a serrodyne optical-frequency translator with shifted-signal to imagesignal discrimination of 52 dB for a 4-MHz frequency shift. The amplitude of the sawtooth driving signal was 10 V peak to peak. Application of a de bias voltage of either polarity was found to cause a substantial reduction in transmitted-light intensity.
We report the results of a systematic study on planar optical waveguides fabricated in z-cut LiNbO3 by proton exchange in benzoic acid. It was found that the refractive index varied with depth and could be accurately modeled by a step index profile with Δn=0.126. Diffusion coefficients have been calculated from mode effective refractive index measurements, assuming a step index profile, and hence a value for the activation energy for the proton exchange process has been deduced. The lowest measured optical propagation loss in single-mode waveguide at a 633-nm wavelength was 2.4 dB/cm.
This article reports new characterization data for large-area (250 lm · 250 lm) back-illuminated planar n-on-p HgCdTe electron-initiated avalanche photodiodes (e-APDs). These e-APDs were fabricated in p-type HgCdTe films grown by liquid-phase epitaxy (LPE) on CdZnTe substrates. We previously reported that these arrays exhibit gain that increases exponentially with reverse bias voltage, with gain-versus-bias curves that are quite uniform from element to element, and with a maximum gain of 648 at -11.7 V at 160 K for a cutoff wavelength of 4.06 lm. Here we report new data on these planar e-APDs. Data from a third LPE film with a longer cutoff wavelength (4.29 lm at 160 K) supports the exponential dependence of gain on cutoff wavelength, for the same bias voltage, that we reported for the first two films (with cutoffs of 3.54 lm and 4.06 lm at 160 K), in agreement with BeckÕs empirical model for gain versus voltage and cutoff wavelength in HgCdTe e-APDs. Our lowest gain-normalized current density at 80 K and zero field-of-view is 0.3 lA/cm 2 at -10.0 V for a cutoff of 4.23 lm at 80 K. We report data for the temperature dependence of gain over 80 K to 200 K. We report, for the first time, the dependence of measured gain on junction area for widely spaced circular diodes with radii of 20 lm to 175 lm. We interpret the variation of measured gain with junction area in terms of an edge-enhanced electric field, and fit the data with a two-gain model having a lower interior gain and a higher edge gain. We report data for the excess noise factor F(M) near unity for gains up to 150 at 196 K. We describe the abrupt breakdown phenomenon seen in most of our devices at high reverse bias.
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