Aaron G. Lind

Maximizing electrical activation of ion-implanted Si in In0.53Ga0.47As

A relationship between the electrical activation of Si in ion-implanted In0.53Ga0.47As and material microstructure after ion implantation is demonstrated. By altering specimen temperature during ion implantation to control material microstructure, it is advanced that increasing sub-amorphizing damage (point defects) from Si+ implantation results in enhanced electrical activation of Si in In0.53Ga0.47As by providing a greater number of possible sites for substitutional incorporation of Si into the crystal lattice upon subsequent annealing.

Comparison of thermal annealing effects on electrical activation of MBE grown and ion implant Si-doped In0.53Ga0.47As

The effect of thermal annealing on the net donor concentration and diffusion of Si in In0.53Ga0.47As is compared for electrically active layers formed by ion implantation versus molecular beam epitaxy (MBE). Upon thermal treatment at temperatures of 700 °C or higher for 10 min, both ion implanted and growth-doped substrates converge to a common net donor solubility. These results indicate that while MBE doped substrates typically exhibit higher active concentrations relative to implanted substrates, the higher active Si concentrations from MBE growth are metastable and susceptible to deactivation upon subsequent thermal treatments after growth. Active Si doping concentrations in MBE doped material and ion-implanted materials are shown to converge toward a fixed net donor solubility limit of 1.4 × 1019 cm−3. Secondary ion mass spectroscopy of annealed samples indicates that the diffusivity of Si in MBE doped substrates is higher than those of ion implanted substrates presumably due to concentration-depende...

Concentration-dependent diffusion of ion-implanted silicon in In0.53Ga0.47As

In contrast to prior reports, evidence of concentration-dependent diffusion is reported for Si implanted In0.53Ga0.47As. The Fickian and concentration-dependent components of diffusivities were extracted using the Florida object oriented process and device simulator. The migration energy for silicon diffusion in In0.53Ga0.47As was calculated to be 2.4 and 1.5 eV for the Fickian and concentration dependent components of diffusion, respectively. A lack of change in diffusivities at given anneal temperatures suggest that transient-enhanced diffusion has not occurred. Due to these findings, silicon diffusion at high doping concentrations (>1 × 1020 cm−3) should be better characterized and understood for future complimentary metal-oxide semiconductor applications.

Under-gate defect formation in Ni-gate AlGaN/GaN high electron mobility transistors

Abstract High electron mobility transistors based on Aluminum Gallium Nitride/Gallium Nitride heterostructures are poised to become the technology of choice for a wide variety of high frequency and high power applications. Their reliability in the field, particularly the reliability of the gate electrode under high reverse bias, remains an ongoing concern, however. Rapid increases in gate leakage current have been observed in devices which have undergone off-state stressing. Scanning Electron Microscopy, scanning probe microscopy, and Transmission Electron Microscopy have been used to evaluate physical changes to the structure of Ni-gated devices as the gate leakage current begins its initial increase. This evaluation indicates the formation of an interfacial defect similar to erosion under the gate observed by other authors. Defect formation appears to be dependent upon electrical field as well as temperature. Transmission Electron Microscopy has been used to demonstrate that a chemical change to the interfacial oxynitride layer present between the semiconductor and gate metal appears to occur during the formation of this defect. The interfacial layer under the gate contact transitions from a mixed oxynitride comprised of gallium and aluminum to an aluminum oxide.

Co-implantation of Al+, P+, and S+ with Si+ implants into In0.53Ga0.47As

Elevated temperature, nonamorphizing implants of Si+, and a second co-implant of either Al+, P+, or S+ at varying doses were performed into In0.53Ga0.47As to observe the effect that individual co-implant species had on the activation and diffusion of Si doping after postimplantation annealing. It was found that Al, P, and S co-implantation all resulted in a common activation limit of 1.7 × 1019 cm−3 for annealing treatments that resulted in Si profile motion. This is the same activation level observed for Si+ implants alone. The results of this work indicate that co-implantation of group V or VI species is an ineffective means for increasing donor activation of n-type dopants above 1.7 × 1019 cm−3 in InGaAs. The S+ co-implants did not show an additive effect in the total doping despite exhibiting significant activation when implanted alone. The observed n-type active carrier concentration limits appear to be the result of a crystalline thermodynamic limit rather than dopant specific limits.

Implantation and Diffusion of Silicon Marker Layers in In0.53Ga0.47As

Continued effort has been placed on maximizing activation while controlling the diffusion of silicon doping in InGaAs for present and future complementary metal-oxide semiconductor devices. In order to explore the diffusion and activation behavior, Si marker layers were grown in InGaAs on InP by molecular beam epitaxy. The nature of Si diffusion was explored using a series of isoelectronic implants to introduce excess point defects near the layer. It was observed that excess interstitials reduce the Si diffusion consistent with a vacancy-driven diffusion mechanism. A diffusion and activation model implemented in the Florida object oriented process simulator has been developed to predict silicon diffusion behavior over a variety of temperatures and times. Using current and previous experimental data and complimentary density functional theory results, the diffusion model employs the SiIII–VIII pair as the primary mechanism for silicon diffusion in InGaAs.

Degradation mechanisms of Ti/Al/Ni/Au-based Ohmic contacts on AlGaN/GaN HEMTs

The degradation mechanism of Ti/Al/Ni/Au-based Ohmic metallization on AlGaN/GaN high electron mobility transistors upon exposure to buffer oxide etchant (BOE) was investigated. The major effect of BOE on the Ohmic metal was an increase of sheet resistance from 2.89 to 3.69 Ω/◻ after 3 min BOE treatment. The alloyed Ohmic metallization consisted 3–5 μm Ni-Al alloy islands surrounded by Au-Al alloy-rings. The morphology of both the islands and ring areas became flatter after BOE etching. Energy dispersive x-ray analysis and Auger electron microscopy were used to analyze the compositions and metal distributions in the metal alloys prior to and after BOE exposure.

Activation of Si implants into InAs characterized by Raman scattering

Studies of implant activation in InAs have not been reported presumably because of challenges associated with junction leakage. The activation of 20 keV, Si+ implants into lightly doped (001) p-type bulk InAs performed at 100 °C as a function of annealing time and temperature was measured via Raman scattering. Peak shift of the L+ coupled phonon-plasmon mode after annealing at 700 °C shows that active n-type doping levels ≈5 × 1019 cm−3 are possible for ion implanted Si in InAs. These values are comparable to the highest reported active carrier concentrations of 8–12 × 1019 cm−3 for growth-doped n-InAs. Raman scattering is shown to be a viable, non-contact technique to measure active carrier concentration in instances where contact–based methods such as Hall effect produce erroneous measurements or junction leakage prevents the measurement of shallow n+ layers, which cannot be effectively isolated from the bulk.

Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

The effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs) was studied. AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm−2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersion observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.

Activation and defect dissolution of non-amorphizing, elevated temperature Si + implants into In 0.53 Ga 0.47 As

A range of implant temperatures from 20 to 300C are studied for fixed 20 keV implant energy and 6E14 cm-2 dose Si implants into In0.53Ga0.47As. Hall effect measurements performed on the samples after rapid thermal annealing reveal that Si implant activation is actually maximized for intermediate implant temperatures from 50-110C that are shown to be non-amorphizing. While these results echo the conclusion of previous studies that elevated temperature Si implants into In0.53Ga0.47As show increased activation over implants that are likely amorphizing, it is clear that there is a temperature window from 50-110C where activation is improved with increasing thermal budget for the dose and energy studied. Calculated Si solubilities of up to 1.3E19 cm-3 and sheet resistances as low as 26 ohm/sq are achieved for a 10 keV 5E14 cm-2 Si implant performed at 80C after 750C 5s annealing.