A hole concentration greater than 1020 cm−3 in GaAs has been achieved using a liquid CCl4 source for carbon in a low-pressure organometallic vapor phase epitaxy system. The resistivity and hole mobility measured at 300 K for a heavily carbon-doped (1.2×1020 cm−3) Hall sample made from a thin (180 nm) epitaxial layer were 8.0×10−4 Ω cm and 65 cm2/V s, respectively. Carbon-doped samples with excellent surface morphology were achieved using a V/III ratio of 22, and growth pressure and temperature of 80 Torr and 600 °C, respectively. A novel photoluminescence technique, based on band-gap shrinkage of heavily doped p+-GaAs, has been shown to be useful for nondestructive measurement of the hole concentration in submicrometer layers.

The redistribution of Cr in semi-insulating GaAs upon annealing at 860 °C can be greatly reduced by eliminating the use of a SiO2 encapsulant. The annealing schedule utilized a controlled atmosphere technique which insured the thermodynamic stability of the GaAs surfaces and had no tendency to getter Cr. The sample annealed with a SiO2 encapsulant showed a secondary-ion-mass-spectroscopy-measured minimum Cr concentration which was lower by a factor of 20–25 than the original, whereas the comparison of an annealed sample without the SiO2 cap had a minimum Cr concentration which was smaller by a factor of 2. The conversion near the surfaces of semi-insulating Cr-doped GaAs to moderately high-conductivity n type upon annealing can be minimized by using the above technique without an encapsulant.

We present experimental evidence that current gain cutoff frequency (ft) values equal to or greater than those achieved with high electron mobility transistors (HEMTs) and pseudomorphic HEMTs can also be achieved by ion-implanted GaAs and InGaAs metal-semiconductor field-effect transistors. These measured ft results clearly suggest that the average electron velocity under the gate is determined primarily by the high-field electron velocity rather than the low-field electron mobility. Hence, we conclude that the transport properties of the two-dimensional electron gas in HEMTs and pseudomorphic HEMTs do not make a significant contribution to the high-frequency and high-speed performance of these devices.

Extensive data are presented on impurity-induced layer disordering (IILD) of AlxGa1−xAs-GaAs quantum-well heterostructures and superlattices that are Si implanted and annealed (Si+-IILD) at three different implant doses. We show that impurity activation is not critical to the layer disordering process and that Si diffusion from the implanted profile initiates Si+-IILD. When the implant dose is as high as φ≥5×1013/cm2 (nSi ≥2×1018/cm3), Si interstitial loops (Si-ILs) form by diffusion and agglomeration of the implanted Si atoms during the initial stages of annealing. If a source of Ga vacancies is provided (e.g., via an As overpressure or SiO2 encapsulation), the Si-ILs dissociate and supply Si atoms for diffusion and hence Si+-IILD during the latter stages of annealing. If a Si3N4 encapsulant is employed, however, fewer Si-ILs form and Si diffusion is inhibited. For an implantation dose as low as φ=1×1012/cm2 (nSi =3×1016/cm3), extensive Si+-IILD is realized via capless annealing and Si-ILs are not observed. It is significant for device applications that the layer-disordered material operates as a cw 77 K photopumped laser, which indicates that the layer averaging (IILD) does not damage the crystal.

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