W. S. Hobson

Ga2O3 films for electronic and optoelectronic applications

Properties of Ga2O3 thin films deposited by electron‐beam evaporation from a high‐purity single‐crystal Gd3Ga5O12 source are reported. As‐deposited Ga2O3 films are amorphous, stoichiometric, and homogeneous. Excellent uniformity in thickness and refractive index was obtained over a 2 in. wafer. The films maintain their integrity during annealing up to 800 and 1200 °C on GaAs and Si substrates, respectively. Optical properties including refractive index (n=1.84–1.88 at 980 nm wavelength) and band gap (4.4 eV) are close or identical, respectively, to Ga2O3 bulk properties. Reflectivities as low as 10−5 for Ga2O3/GaAs structures and a small absorption coefficient (≊100 cm−1 at 980 nm) were measured. Dielectric properties include a static dielectric constant between 9.9 and 10.2, which is identical to bulk Ga2O3, and electric breakdown fields up to 3.6 MV/cm. The Ga2O3/GaAs interface demonstrated a significantly higher photoluminescence intensity and thus a lower surface recombination velocity as compared to ...

Photoexcited escape probability, optical gain, and noise in quantum well infrared photodetectors

We present a detailed and thorough study of a wide variety of quantum well infrared photodetectors (QWIPs), which were chosen to have large differences in their optical and transport properties. Both n‐ and p‐doped QWIPs, as well as intersubband transitions based on photoexcitation from bound‐to‐bound, bound‐to‐quasicontinuum, and bound‐to‐continuum quantum well states were investigated. The measurements and theoretical analysis included optical absorption, responsivity, dark current, current noise, optical gain, hot carrier mean free path, net quantum efficiency, quantum well escape probability, quantum well escape time, as well as detectivity. These results allow a better understanding of the optical and transport physics and thus a better optimization of the QWIP performance.

Demonstration of enhancement-mode p- and n-channel GaAs MOSFETS with Ga2O3(Gd2O3) As gate oxide

Abstract We report the demonstration of both enhancement-mode p - and n -channel GaAs metal oxide semiconductor field effect transistors (MOSFETs) on GaAs semi-insulating substrates using high quality Ga 2 O 3 (Gd 2 O 3 ) as the gate dielectric and the conventional ion-implant technology. The source and drain regions were selectively implanted with Zn or Si for low resistance ohmic contacts for p - or n -MOSFETs, respectively. AuBe/Pt/Au, Ge/Mo/Au-Ge/Mo/Au, and Ti/Pt/Au were deposited for p - and n -ohmic contacts and gate electrode, respectively. The devices, with a 4 × 50 μ m 2 gate geometry, exhibit an extrinsic transconductance of 0.18 and 0.1 mS/mm for p - and n -MOSFETs, respectively, and an excellent gate breakdown field greater than 3 MV cm −1 .

Ga 2 O 3 (Gd 2 O 3 )/InGaAs enhancement-mode n-channel MOSFETs

We have demonstrated the first Ga/sub 2/O/sub 3/(Gd/sub 2/O/sub 3/) insulated gate n-channel enhancement-mode In/sub 0.53/Ga/sub 0.47/As MOSFETs on InP semi-insulating substrate. Ga/sub 2/O/sub 3/(Gd/sub 2/O/sub 3/) was electron beam deposited from a high purity single crystal Ga/sub 5/Gd/sub 3/O/sub 12/ source. The source and drain regions of the device were selectively implanted with Si to produce low resistance ohmic contacts. A 0.75-/spl mu/m gate length device exhibits an extrinsic transconductance of 190 mS/mm, which is an order of magnitude improvement over previously reported enhancement-mode InGaAs MISFETs. The current gain cutoff frequency, f/sub t/, and the maximum frequency of oscillation, f/sub max/, of 7 and 10 GHz were obtained, respectively, for a 0.75/spl times/100 /spl mu/m/sup 2/ gate dimension device at a gate voltage of 3 V and drain voltage of 2 V.

High-power laser light source for near-field optics and its application to high-density optical data storage

A laser light source for high-resolution near-field optics applications with an output power exceeding 1 mW (104 times the power from previous sources) and small (300 nm square to less than 50 nm square) output beam size is demonstrated. The very-small-aperture laser (VSAL) tremendously expands the range of applications possible with near-field optics and increases the signal-to-noise ratios and data rates obtained in existing applications. As an example, 250-nm-diam marks corresponding to 7.5 Gb/in.2 storage density have been recorded and read back in reflection and transmission on a rewritable phase-change disk at 24 Mb/s with a 250-nm-square aperture VSAL. VSALs potentially enable data storage densities of over 500 Gb/in.2 (up to 100 times today’s magnetic or optical storage densities).

Carbon doping of III-V compounds grown by mombe

Recent advances in heterostructure bipolar transistor (HBT) technology have created a need for p-type doping at levels ≥1020 cm-3. We have achieved p-type doping levels as high as 5×1020 cm-3 using C, which is introduced through the use of trimethylgallium (TMG) during metalorganic molecular beam epitaxy (MOMBE) growth of GaAs. By utilizing the atomic planar doping method, we have also been able to grow C-doped spikes with hole concentrations as high as 7×1019 cm-3, with a full width at half maximum of ∼50 A at 300 K. This level is among the highest reported for planar doping. By switching out the TMG, and switching in the triethylgallium (TEG) to continue to growth of C-free GaAs, we have grown sandwich-type structures with C levels of 1020 cm-3, which fall off within 210 A to C levels of <1017 cm-3. High temperature annealing of such structures reveals a C diffusion coefficient of <10-16 cm2 s-1 at 950°C, in agreement with other reports. The electrical properties of layers annealed at high temperatures appear to be influenced by the presence of strain arising from the high C concentration. X-ray diffraction patterns of 3 μm layers doped in excess of 1020 cm-3 show a lattice constant which corresponds roughly to that calculated by assuming a Vegard law mixture of GaAs and 0.7% GaC. Preliminary results of C-doping of InGaAs will also be discussed. Finally, the usefulness of carbon doping has been demonstrated in ohmic contact formation, Schottky barrier height enhancement in MESFETs and as the base layer in HBTs.

Vertical-cavity surface-emitting lasers flip-chip bonded to gigabit-per-second CMOS circuits

We describe the first integration of vertical-cavity surface-emitting laser arrays with gigabit-per-second CMOS circuits via flip-chip bonding.

CCl4 doping of GaN grown by metalorganic molecular beam epitaxy

Hole concentrations up to 1017 cm−3 are achieved in GaN doped with C from a CCl4 source during metalorganic molecular beam epitaxy at 700 °C. The hole mobility under these conditions is 103 cm2 V−1 s−1 at 300 K. The deposition rate of the GaN is reduced by addition of CCl4 to the growth chemistry even at low flow rates and net etching is observed for a halocarbon flow above 1.1 sccm under our conditions. Annealing up to 800 °C did not increase the hole concentration indicating that residual hydrogen passivation of the acceptors is not significant when employing a He carrier gas for transporting the group III metalorganic precursor (triethylgallium).

Plasma etching of III–V semiconductors in CH4/H2/Ar electron cyclotron resonance discharges

We have investigated the etch rates, residual lattice damage, surface morphologies, and chemistries of InP, InGaAs, AlInAs, and GaAs plasma etched in electron cyclotron resonance (ECR) CH4/H2/Ar discharges. The etch rates of InP and InGaAs increase linearly with additional rf biasing of the substrate, and are approximately a factor of 2 faster than for GaAs. Under our conditions the etch rate of Al0.52Ga0.48As is very low (∼25 A min−1) even for the addition of 100 V rf bias. In all of these materials the residual damage layer remaining after dry etching is very shallow (∼20 A) as evidenced from Schottky barrier height and photoluminescence measurements combined with wet chemical etching. InP shows significant P depletion with the addition of rf biasing during the ECR etching while GaAs retains a near‐stoichiometric surface. Hydrogen passivation of shallow donors in n‐type GaAs occurs to a depth of ∼3000 A during exposure to the CH4/H2/Ar discharge for long periods (60 min). The surface morphologies in the...

GaAs/AlGaAs microdisk lasers

GaAs/AlGaAs microdisk lasers have been achieved using continuous optical pumping at 80 K. Surface passivation with a new sulfur/SiNx process is required in order to achieve steady‐state lasing. Approximately 15% of the spontaneous emission is coupled into the lasing mode.