M.E. Sherwin

Evidence of a thermally stable carbon-nitrogen deep level in carbon-doped, nitrogen-implanted, GaAs and AlGaAs

Nitrogen ion implantation is shown to form high resistivity regions (ps ≥ 1 × 1010 Ω/) in C-doped GaAs and Al0.35Ga0.65As that remains compensated after a 900°C anneal. This is in contrast to oxygen or fluorine implantation in C-doped GaAs which both recover the initial conductivity after a sufficiently high temperature anneal (800°C for F and 900°C for O). In C-doped Al0.35Ga0.65As N- and O-implant isolation is thermally stable but F-implanted samples regain the initial conductivity after a 700°C anneal. A dose dependence is observed for the formation of thermally stable N-implant compensation for both the GaAs and AIGaAs samples. A C-N complex is suggested as the source of the compensating defect level for the N-implanted samples. Sheet resistance data vs anneal temperature and estimates of the depth of the defect levels are reported. This result will have application to heterojunction bipolar transistors and complementary heterostructure field effect transistor technologies that employ C-doped AIGaAs or GaAs layers along with high temperature post-implant isolation processing.

Comparison of Mg and Zn gate implants for GaAs n-channel junction field effect transistors

Zinc and magnesium implants into GaAs were profiled with secondary ion mass spectroscopy and etching capacitance-voltage to measure the as-implanted and annealed profiles for the eventual formation of shallow p+/n junction gates for junction field effect transistors (JFETs). The larger mass of the zinc ions results in shorter projected range with significantly less tailing than magnesium implants. High dose, shallow zinc implants annealed under tungsten gate metal showed good activation with negligible diffusion. The improved profile of the zinc implant, as compared to a similar magnesium implant, allowed a tighter JFET design with increased performance. Zn gated n-channel enhancement mode GaAs JFETs with 0.9 µm gate lengths showed transconductances up to 200 mS/ mm with a ft of 18 GHZ and a fmax of 37 GHz. The performance of these self-aligned fully implanted JFETs compare favorably with comparably sized implanted MESFETs.

An all implanted self-aligned enhancement mode n-JFET with Zn gates for GaAs digital applications

An all implanted self-aligned n-channel JFET fabrication process is described where Zn implantation is used to form the p/sup +/ gate region. A refractory metal (W) gate contact is used to allow subsequent high temperature activation of the self-aligned Si source and drain implant. 0.7 /spl mu/m JFETs have a maximum transconductance of 170 mS/mm with a saturation current of 100 mA/mm at a gate bias of 0.9 V. The p/sup +//n homojunction gate has a turn on voltage of 0.95 V at a current of 1 mA/mm. The drain-source breakdown voltage is 6.5 V. Microwave measurements made at a gate bias of 1 V show an f/sub t/ of 19 GHz with an f/sub max/ of 36 GHz. These devices show promise for incorporation in both DCFL and complementary logic circuits.<<ETX>>

Complementary GaAs junction-gated heterostructure field effect transistor technology

The first circuit results for a new GaAs complementary logic technology are presented. The technology allows for independently optimizable p- and nchannel transistors with junction gates. Excellent loaded gate delays of 179 ps at 1.2 V and 319 ps at 0.8 V have been demonstrated at low power supply voltages. A power-delay product of 8.9 fJ was obtained at 0.8 V.

Ion-implanted GaAs JFETs with f/sub t/>45 GHz for low-power electronics

GaAs Junction Field Effect Transistors (JFETs) are reported with gate lengths down to 0.3 /spl mu/m. The structure is fully self-aligned and employs all ion implantation doping. p/sup +/-gate regions are formed with either Zn or Cd implants along with a P co-implantation to reduce diffusion. The source and drain implants are engineered with Si or SiF implants to minimize short channel effects. 0.3 /spl mu/m gate length JFETs are demonstrated with a subthreshold slope of 110 mV/decade along with an intrinsic unity current gain cutoff frequency as high as 52 GHz.

n‐type ion implantation doping of AlxGa1−xAs (0⩽x⩽0.7)

Si‐implant activation characteristics in AlxGa1−xAs for Al compositions of 0%–70% AlAs are presented for doses of 5.6×1012 and 2.8×1013 cm−2 at 100 keV. For both doses, the effective activation efficiency (ηeff) is relatively constant from 0% to 20% AlAs (ηeff=64% for 5.6×1012 cm−2 and 37% for 2.8×1013 cm−2 for 20% AlAs), goes through a minimum at 35% AlAs (ηeff=6.6% for 5.6×1012 cm−2 and 2.5% for 2.8×1013 cm−2), and then increases towards 70% AlAs (ηeff=52.8% for 5.6×1012 cm−2 and 31.1% for 2.8×1013 cm−2). The results are explained based on the compositional dependence of the ionization energy and conduction band density‐of‐states of AlGaAs. The effects of P coimplantation is also studied but demonstrates no significant enhancement of the activation efficiency of Si implantation for 0%–70% AlAs. Finally, data are presented for Se implantation in Al0.2Ga0.8As with a maximum effective activation efficiency of 5.6% achieved.

Non-alloyed, refractory metal contact optimization with shallow implantations of Zn and Mg

Refractory metal contacts to GaAs show great promise for stability during high temperature processing and for high reliabiltiy. In this paper, we report on a study of sputtered W and W-Si contacts to ion-implanted p-GaAs with both Zn and Mg implantations. This study focused on refractory contacts to shallow implanted contact layers that are suitable for devices such as junction field effect transistors and heterojunction bipolar transistors. The very different energy loss mechanisms of Zn and Mg ions result in different levels of implant damage, which is studied by varying the annealing temperatures and measuring the effects on contact and sheet resistances with the transmission line method