Growth of fully doped Hg 1−x Cd x Te heterostructures using a novel iodine doping source to achieve improved device performance at elevated temperatures

Band gap engineered Hg1−xCdxTe (MCT) heterostructures should lead to detectors with improved electro-optic and radiometric performance at elevated operating temperatures. Growth of such structures was accomplished using metalorganic vapor phase epitaxy (MOVPE). Acceptor doping with arsenic (As), using phenylarsine (PhAsH2), demonstrated 100% activation and reproducible control over a wide range of concentrations (1 × 1015 to 3.5 × 1017 cm−3). Although vapor from elemental iodine showed the suitability of iodine as a donor in MC.T, problems arose while controlling low donor concentrations. Initial studies using ethyliodide (EtI) demonstrated that this source could be used successfully to dope MCT, yielding the properties required for stable heterostructure devices, i.e. ≈100% activation, no memory problems and low diffusion coefficient. Cryogenic alkyl cooling or very high dilution factors were required to achieve the concentrations needed for donor doping below ≈1016cm−3 due to the high vapor pressure of the alkyl. A study of an alternative organic iodide source, 2-methylpropyliodide (2 MePrI), which has a much lower vapor pressure, improved control of low donor concentrations. 2 MePrI demonstrated the same donor source suitability as EtI and was used to control iodine concentrations from ≈ 1 × 1015 to 5 × 1017cm−3. The iodine from both sources only incorporated during the CdTe cycles of the interdiffused multilayer process (IMP) in a similar manner to both elemental iodine and As from PhAsH2. High resolution secondary ion mass spectroscopy analysis showed that IMP scale modulations can still be identified after growth. The magnitude of these oscillations is consistent with a diffusion coefficient of≈7 × 10−16cm2s−1 for iodine in MC.T at 365°C. Extrinsically doped device heterostructures, grown using 2 MePrI, have been intended to operate at elevated temperatures either for long wavelength (8–12 smm) equilibrium operation at 145K or nonequilibrium operation at 190 and 295K in both the 3–5 µ and 8–12 µ wavelength ranges. Characterization of such device structures will be discussed. Linear arrays of mesa devices have been fabricated in these layers. Medium wave nonequilibrium device structures have demonstrated high quantum efficiencies and R0A = 37 Ωcm2 for λco = 4.9 µ at 190K.