In Situ Band-Edge Monitoring of Cd1−yZnyTe Substrates for Molecular Beam Epitaxy of HgCdTe
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We demonstrate the benefits of in situ band-edge monitoring of CdZnTe substrates for molecular beam epitaxy (MBE). The production of large-area Cd1−yZnyTe(211)B substrates up to and exceeding 8 × 8 cm2 brings new challenges from the perspective of MBE growth of Hg1−xCdxTe. Localized variation of the Zn concentration, even less than y = 0.01, can potentially cause variation in lattice-misfit with the HgCdTe epi-layers potentially resulting in ∼ 10 × difference in etch-pit density. Variation in Zn concentration is expected to be greater over larger substrates, and thus local differences in dislocation density may also be expected. The substrate Zn concentration has been determined using in situ band-edge measurement prior to nucleation of HgCdTe. Ex situ infrared transmission spectra has been used to confirm the validity of in situ band-edge wavelength measurements. We also examine the usefulness of band-edge thermometry (BET), for monitoring substrate temperature during Te/oxide desorption and for nucleation of HgCdTe epi-layers. In principle, knowledge of the exact Zn content across the largest area of the substrate, allows for tuning growth parameters to maximize yield of perfectly lattice-matched material.
KeywordsCdZnTe substrate HgCdTe band-edge MBE in situ metrology
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