Deep levels in GaAs/Al0.78Ga0.22As heterostructures

A preliminary study of growth interruption effects on the GaAs/AlGaAs layers is reported. Deep level transient spectroscopy (DLTS) is performed on Al Schottky barrier devices fabricated on Si-doped, isotype GaAs/Al0.78Ga0.22As heterostructures grown by molecular beam epitaxy (MBE), both with (200 s) and without, growth interruption. Our spectra extending from ∼15 to 300 K show four peaks corresponding to deep level defects with thermal activation energies (EA): 0.09, 0.32, 0.42 and 0.52 eV, which are detected in both types of samples (close to and) above liquid nitrogen temperature, although with different relative concentrations. Comparison with reported work on GaAs/AlxGa1−xAs samples with different compositions (x) shows that latter two of these deep levels are counterparts of the levels, P3–P4, earlier observed in MBE grown AlxGa1−xAs materials with Al content different than that used here. However, the deep level spectra of our samples show dramatic differences for the growth interrupted and uninterrupted samples in the temperature range below 77 K. Whereas the samples prepared without growth interruption show a prominent, hitherto unobserved, positive (majority carrier emission) peak, P0 (EA=0.029 eV), with shoulders on both higher and lower temperature flanks, the samples with growth interruption show a pronounced negative peak, apparently corresponding to a deep level with EA=0.031 eV, in the same temperature region, under similar measurement conditions. The deep-level characteristics, including emission rate signatures and apparent capture cross-sections, are determined for the observed features using the thermal emission rate data. Some interesting additional features related to depth profiles of deep levels, bias effects and charge-induced metastability effects are also reported.