Thermally annealed GaN nucleation layers and the devicequality metal organic chemical vapor deposition growth of Sidoped GaN films on (00.1) sapphire

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.

Transmission electron microscopy (TEM) is widely used for the characterization of the microstructure of Hg1−xCdxTe epilayers. Traditional TEM sample preparation methods, which usually involve argon ion milling, can easily cause damage to the material, and the size and density of the induced defects depend on the milling conditions. In this work, the structural damage caused by argon ion milling of Hg1−xCdxTe epilayers has been investigated. Multilayer samples with different Hg concentrations, as grown by molecular beam epitaxy, and p-n heterojunctions, as grown by liquid-phase epitaxy, have been examined. It is shown that, in addition to the milling conditions, the extent of the ion-induced damage depends sensitively on the Hg concentration of the Hg1−xCdxTe alloy as well as the epilayer growth conditions (i.e., Hg rich or Te rich). A possible mechanism that explains these results is briefly discussed.

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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