H. B. Dietrich

Fabrication and characterization of GaN FETs

Abstract The current status of GaN-based FET technology and performance is reviewed. The fabrication details and the dc and microwave characteristics of GaN MESFETs that utilize Si-doped channels on semi-insulating buffer layers are presented. MESFETs with a 0.8 μm gate have exhibited an f T and f max of 6 and 14 GHz, respectively. These devices have excellent pinchoff characteristics and a source-drain breakdown voltage of over 85 V. A high-field current-collapse phenomenon is observed in these MESFETs in the absence of light. The characteristics of this current collapse as a function of temperature, illuminating wavelength, and time are described. A model describing the current collapse in terms of hot electron injection into the buffer layer is presented.

H, He, and N implant isolation of n‐type GaN

The effect of ion‐implantation‐induced damage on the resistivity of n‐type GaN has been investigated. H, He, and N ions were studied. The resistivity as a function of temperature, implant concentration, and post‐implant annealing temperature has been examined. Helium implantation produced material with an as‐implanted resistivity of 1010 Ω‐cm. He‐implanted material remained highly resistive after an 800 °C furnace anneal. The damage associated with H implantation had a significant anneal stage at 250 °C and the details of the as‐implanted resistivity were sample dependent. N implants had to be annealed at 400 °C to optimize the resulting resistivity but were then thermally stable to over 800 °C. The 300 °C resistivity of thermally stabilized He‐ and N‐ implanted layers was 104 Ω‐cm, whereas for H‐implanted layers the 300 °C resistivity was less than 10 Ω‐cm.

Silicon implantation into GaAs : observations of dose rate dependent electrical activation and damage

The electrical activation of ion‐implanted silicon in GaAs has been studied as a function of dose rate (i.e., ion‐current density). For a fluence of 1014 cm−2, the Hall sheet carrier activation is shown to depend strongly on the dose rate at which the implant was carried out. Carrier concentrations of 7×1018 cm−3 were produced at a 50×10−9 A/cm2 ion‐current density. The variation in electrical activation is believed to be the result of a dose rate dependence of the ion‐induced damage of GaAs which can be clearly seen in Rutherford backscattering (RBS) channeling measurements of 1015 cm−2 implants.

Photoluminescence and magnetic resonance studies of Er3+ in MeV ion-implanted GaAs

The effects of post‐implantation annealing have been studied in MeV Er‐implanted GaAs by monitoring the Er3+ electron paramagnetic resonance (EPR) signal as well as the Er3+ and near‐band‐edge photoluminescence (PL) spectra as a function of the anneal temperature. Er3+ PL is observed from several distinct Er sites in the annealed material. In addition, the observed dependences upon anneal temperature suggest that the Er3+ PL is emitted from centers that are not in the Er3+ state at equilibrium. Absolute EPR measurements of the Er3+ concentration indicate that only a small fraction (<0.1%) of the Er in the sample is Er3+.

Ion‐implanted n‐channel InP metal semiconductor field‐effect transistor

Device‐quality n‐type layers have been produced by ion implantation in Fe‐doped semi‐insulating InP. 29Si has been used as the dopant and anneals were carried out with the aid of a multiple‐layered encapsulant consisting of plasma‐deposited Si3N4 and pyrolytic P‐doped SiO2. These layers have been used to make n‐channel MESFET’s for which gains of 13.7 and 9.8 dB were measured at 8 and 10 GHz, respectively. The gate metallization for these devices was Au. Low‐leakage currents and adequate gate breakdown characteristics were observed.

In0.53Ga0.47As metal‐semiconductor‐metal photodetector using proton bombarded p‐type material

Metal‐semiconductor‐metal (MSM) photodetectors have been fabricated using as‐grown and proton‐bombarded p‐type In0.53Ga0.47As. Proton bombardment caused a decrease in the dark current, an increase in the breakdown voltage, and an improvement in the speed of the MSM detector. The dark current of the MSM detector with 3×1015 cm−3 proton bombardment is 10 nA at 2 V and 300 nA at 5‐V bias. The dc responsivity is 0.7 A/W and impulse response full width at half maximum is 160 ps for 1.3 μm radiation at 5 V bias.

High-energy Si implantation into InP:Fe

High‐energy Si implantations were performed into InP:Fe at energies ranging from 0.5 to 10 MeV for a dose of 3×1014 cm−2, and at 3 MeV for the dose ranging from 1×1014 to 2×1015 cm−2. The first four statistical moments of the Si‐depth distribution, namely range, longitudinal straggle, skewness, and kurtosis, were calculated from the secondary‐ion mass spectrometry (SIMS) data of the as‐implanted samples. These values were compared with the corresponding trim‐89 calculated values. SIMS depth profiles were closely fitted by Pearson IV distributions. Multiple implantations in the energy range from 50 keV to 10 MeV were performed to obtain thick n‐type layers. Variable temperature/time halogen lamp rapid thermal annealing (RTA) cycles and 735 °C/10‐min furnace annealing were used to activate the Si implants. No redistribution of Si was observed for the annealing cycles used in this study. Activations close to 100% were obtained for 3×1014‐cm−2 Si implants in the energy range from 2 to 10 MeV for 875 °C/10‐s R...

Observation of ion‐implantation‐damage‐created n‐type conductivity in InP after high‐temperature annealing

The conductivity and the impurity profiles of InP implanted with dopant ions (Si,Be) or non dopant ions (B,H,N,O,P) have been investigated. Experiments have been done in substrates with and without Fe doping. Low‐temperature, short‐time annealing of implanted Si and Be reveals an n‐type distribution of carriers which cannot be accounted for on the basis of implant activation. In order to examine the contribution without the carriers originating from the dopant ions, the behavior of electrically inactive B, H, N, O, and P, implants was investigated. Implantation of these ions into semi‐insulating InP introduced n‐type doping in the 1×1016 cm3 range after an anneal above 450 °C. For H, O, N, and P ions, the n‐type conductivity could be eliminated by annealing at higher temperatures. However, boron anneals up to 750 °C did not eliminate the n‐type conductivity. The n‐type carrier profiles tracked the ion profiles. The carrier profile is influenced by the redistribution of the Fe during annealing; however, th...

Implantation damage in GaAs‐AlAs superlattices of different layer thickness

We report that two GaAs‐AlAs superlattices of different layer thickness show dramatically different crystal damage when ion irradiated under identical conditions. The samples, held at 77 K, were implanted with 100 keV 28Si at doses of 3×1013 cm−2 to 1×1015 cm−2. Ion channeling results show amorphization threshold doses of 1×1015 cm−2 for the 7.0 nm GaAs‐8.5 nm AlAs superlattice and 4×1014 cm−2 for the 3.5 nm GaAs‐5.0 nm AlAs superlattice. At low doses, the shorter period superlattice was more robust, with no damage peak observed in ion channeling spectra for doses as high as 1×1014 cm−2. For a dose of 7×1013 cm−2, double crystal x‐ray diffraction measurements show a 6 arcsec broadening of the (004) peak, relative to that of the unimplanted sample, for both superlattices. However, only the finer period superlattice exhibits a broadening (10 arcsec) of the (224) diffracted peak indicating a distortion in an additional direction. A mechanism involving the formation of slightly misaligned crystal domains is s...

Gallium arsenide transferred‐electron devices by low‐level ion implantation

Extended n‐type layers have been produced in semi‐insulating GaAs by the activation of Si implanted to atomic concentrations as low as 6×1016 cm−3. Active layers were obtained in two types of undoped (no intentional dopants introduced during the growth process) semi‐insulating GaAs. These were bulk GaAs grown by the liquid encapsulated Czochralski method and epitaxial layers grown by chemical vapor deposition. Three terminal transferred‐electron devices were fabricated in a completely planar geometry. Gunn domain triggering by the gate resulted in dc negative resistance current dropback between 20% and 40%. High‐frequency negative resistance was observed in the 2–7 GHz range.