The pyrolysis reactions of di-isopropyl telluride and dimethyl cadmium, both alone and in combination and with and without mercury, have been studied using the technique of gas chromatography-mass spectrometry (GC-MS). For example, whtn mercury and dimethyl cadmium are mixed in hydrogen at the growth temperature (370 C), the volatile products observed are methane, ethane and dimethyl mercury. In contrast, when di-isopropyl telluride is substituted for the cadmium precursor in this reaction, the products observed are propane, propene and 2,3-dimethylbutane with no volatile mercury-containing compounds. Heating the two organometallic precursors together at the growth temperature in the absence of mercury gives products expected from the pyrolysis of each one alone plus a number of interaction products such as 2-methylpropane. The results of these studies will be presented, a mechanism for the reactions proposed and the implications for MOVPE growth discussed.
Dual waveband infrared detectors can be relatively complicated structures requiring stacking of single waveband detectors. The paper discusses variants of the back-to-back diode structure, which allows the detected waveband to be selected simply by changing the polarity of the bias. Results are presented for two structures: a dual waveband structure for two bands in the mid-infrared region and a dual mid-long waveband structure. The spectra are modeled using a method that takes account of interdiffusion between the layers. Radiative cross-talk is estimated for both of the structures and good agreement is found between the theoretical and measured spectra.
Long-wavelength HgCdTe heterostructures on silicon (100) substrates have been grown using metal-organic vapor phase epitaxy. Test diodes have been fabricated from this material using mesa technology and flip-chip bonding. We have demonstrated excellent resistance-area product characteristics for diodes with a 10.2μm cutoff wavelength. R0A values approaching 103Ωcm2 at 80K have been measured and the resistance-area product maintained above 102Ωcm2 at 1V reverse bias. Variable temperature R0A values correspond to expected generation-recombination loss mechanisms between 60 and 120K. Current-voltage characteristics of two diodes at opposite sides of an array indicate that a very uniform imaging long-wavelength infrared array could be fabricated from this material.
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