ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Improved growth conditions by molecular-beam epitaxy (MBE) and fabrication of state-of-the-art AlGaAs/GaAs selectively doped heterostructure transistors (SDHTs) and ring oscillators on Si substrates are reported. In MBE growth, use of minimum As4:Ga flux ratio during initial nucleation combined with in situ thermal cycles gave a marked improvement in material quality. With this method, FWHM of x-ray rocking curves was measured as low as 135 arcsec for a 3.5-μm-thick GaAs layer on Si. Although 3-μm-thick undoped GaAs buffer layers on p-type Si substrates were fully depleted under a Schottky contact, a parallel n-type conduction path confined in a thin region (〈0.1 μm) near the GaAs/Si interface was sometimes observed whose sheet density (1012–1013 cm−2) and mobility (600–900 cm2 V−1 s−1) were independent of temperature between 300 and 77 K. This parallel conduction was successfully prevented by doping 0.1 μm GaAs with 5–10×1016 cm−3 Be atoms near the interface. In AlGaAs/GaAs selectively doped heterostructures, for a sheet density of 1012 cm−2, a mobility as high as 53 500 cm2 V−1 s−1 at 77 K was obtained, as against a mobility of ∼70 000 cm2 V−1 s−1 for a similar structure on GaAs substrates. For 1-μm-gate-length SDHTs, maximum transconductances of 220 and 365 mS/mm were measured at 300 and 77 K, respectively. A minimum propagation delay time τd of 28 ps/stage was measured at 300 K for ring oscillators at 1.1 mW/stage power dissipation. τd decreased to 17.6 ps/stage at 77 K. From microwave S-parameter measurements at 300 K, current gain and power gain cutoff frequencies of 15 and 22 GHz, respectively, were measured. These results are comparable to that of SDHT technology on GaAs substrates.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.345529
