Photodiodes responding in the 0.8-2.3 micrometers wavelength range are of interest in a wide range of applications, from wind- shear detection systems which use eyesafe 2.1 micrometers lasers to differential absorption LIDAR aerosol measurements of CO2. In this paper, we report on uncooled, broadband, 2.25 micrometers lattice-mismatched 0.55eV In0.72Ga0.28As photodiode arrays, in which the cutoff wavelength has been 'extended' from the 1.65 micrometers which is standard for 0.74eV In0.53Ga0.47As lattice-matched to InP wafers. InxGa1-xAs step-grading layers were used to transition from the InP wafer to the final In0.72Ga0.28As photodiode material during the metal organic chemical vapor deposition epitaxial growth. Linear 64 X 1 photodiode arrays were made with an independently-verified external quantum efficiency above 50 percent from 0.8 to 2.2 micrometers using MgF2/ZnS dual layer antireflection coating. Average 300 degree K area-normalized dark current for these N/P diodes was 5 X 10-5 A/cm2 at 10mV reverse bias.
We report on the recent growth by Atomic Layer Epitaxy (ALE) of device quality Al0.3Ga0.7As in a modified commercial reactor. A standard Emcore reactor was altered by the installation of baffles to prevent mixing of the reactant gas streams and a computer controlled servo motor to allow for a nonlinear rotation cycle. By varying the V/III ratio and the exposure time to the reactant gases it is possible to control the background carbon doping from high resistivity to p equals 1 X 1020 cm-3, without the need for an additional p-type source. Since low background doping was also achieved, silane was used to obtain n-type Al0.3Ga0.7As as high as n equals 1 X 1018 cm-3. The room temperature Hall mobility of the n-type Al0.3Ga0.7As films varied from 1200 to 3700 cm2/V(DOT)sec. Photoluminescence and preliminary doping results are presented and discussed.
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