J. M. Kuo

Relaxed GexSi1−x structures for III–V integration with Si and high mobility two‐dimensional electron gases in Si

To obtain a large lattice constant on Si, we have grown compositionally graded GexSi1−x on Si. These buffer layers have been characterized with electron‐beam‐induced current, transmission electron microscopy, scanning electron microscopy, x‐ray diffraction, and photoluminescence to determine the extent of relaxation, the threading dislocation density, the surface morphology, and the optical properties. We have observed that it is possible to obtain completely relaxed GexSi1−x layers with 0.1<x<1, threading dislocation densities of 105–5 × 106 cm−2, and with bulk GexSi1−x optical properties. Calculations show that gradually graded layers grown at relatively high temperatures can remain in equilibrium throughout growth, thereby avoiding strain buildup and the introduction of more threading dislocations through dislocation nucleation. It is also shown that the degree of surface crosshatch is related to inhomogeneous strain fields in the epilayer and to the thickness at which dislocations are introduced. Thes...

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.

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.

Normal incidence hole intersubband absorption long wavelength GaAs/AlxGa1−xAs quantum well infrared photodetectors

The first long wavelength quantum well infrared photodetector based on valence band intersubband absorption holes is demonstrated. A normal incidence quantum efficiency of η=28% and detectivity of D*λ=3.1×1010 cm √Hz/W at T=77 K, for a cutoff wavelength λc=7.9 μm, have been achieved.

Beryllium δ doping of GaAs grown by molecular beam epitaxy

Spatial localization of Be in δ‐doped GaAs within few lattice constants (<20 A) is achieved at low growth temperatures for concentrations N2DBe <1014 cm−2 as indicated by capacitance‐voltage profiles and secondary ion mass spectroscopy. At elevated growth temperatures and at higher Be concentrations, significant spreading of the dopants occurs and is explained by (i) Fermi‐level pinning‐induced segregation, (ii) repulsive Coulomb interaction of dopants, and (iii) diffusion. The highest Be concentration achieved at low growth temperatures exceeds 2×1020 cm−3 and is limited by repulsive dopant interaction. It is shown that the repulsive Coulomb interaction results in a correlated, nonrandom dopant distribution. The diffusion coefficient of Be in GaAs is determined and is found to be much lower than previously reported.

Demonstration of submicron depletion-mode GaAs MOSFETs with negligible drain current drift and hysteresis

We successfully fabricated submicron depletion-mode GaAs MOSFETs with negligible hysteresis and drift in drain current using Ga/sub 2/O/sub 3/(Gd/sub 2/O/sub 3/) as the gate oxide. The 0.8-/spl mu/m gate-length device shows a maximum drain current density of 450 mA/mm and a peak extrinsic transconductance of 130 mS/mm. A short-circuit current gain cutoff frequency (f/sub T/) of 17 GHz and a maximum oscillation frequency (f/sub max/) of 60 GHz were obtained from the 0.8 /spl mu/m/spl times/60 /spl mu/m device. The absence of drain current drift and hysteresis along with excellent characteristics in the submicron devices is a significant advance toward the manufacture of commercially useful GaAs MOSFETs.

Spatial resolution of the capacitance‐voltage profiling technique on semiconductors with quantum confinement

The spatial resolution of the capacitance‐voltage profiling technique on semiconductors with one‐dimensional quantum confinement is shown to be given by the spatial extent of the wave function. The Debye length limitation does not apply. Capacitance‐voltage profiles on δ‐doped GaAs of density 4–4.5×1012 cm−2 exhibit widths of 20 and 48 A for p‐ and n‐type impurities, respectively. The profiles agree with the theoretical resolution function and with Be and Si profiles measured by secondary‐ion mass spectroscopy. It is further shown that the saturation of the free‐carrier density of highly Si δ‐doped GaAs grown by molecular beam epitaxy is due to inactive Si impurities

Necessity of Ga prelayers in GaAs/Ge growth using gas-source molecular beam epitaxy

We have investigated the gas‐source molecular beam epitaxy growth of GaAs on a (001) Ge surface, off‐cut 6° towards the [110]. Initiation of GaAs on Ge with the typical procedure of using a self‐terminating As layer invariably produces poor GaAs surface morphology and generates a plethora of antiphase boundaries, despite the large miscut of the (001) surface. However, initiation of GaAs growth with approximately 1 ML (monolayer) of Ga results in single‐domain films with excellent surface morphology. We conclude that the Ga monolayer prevents the Ge surface from forming a high step density surface which is established when Ge is exposed to As2.

Theory and experiment of capacitance-voltage profiling on semiconductors with quantum-confinement

The resolution of the Capacitance-Voltage (C-V) technique on semiconductors with quantum-confinement is shown to be given by the spatial extent of the wave function which represents the electron (hole) system. The classical Debye-length-broadening of the C-V technique is shown to be invalid in the quantum-confinement regime. Capacitance-voltage profiles on δ-doped GaAs exhibit a full-width at half-maximum of 20 and 40Å forp-type andn-type impurities, respectively. The experimental C-V profiles on δ-doped GaAs agree with theory and demonstrate that impurities are spatially localized on the length scale of the lattice constant.

Depletion mode GaAs metal–oxide–semiconductor field effect transistors with Ga2O3(Gd2O3) as the gate oxide

We have successfully fabricated depletion mode GaAs metal–oxide–semiconductor field effect transistors using Ga2O3(Gd2O3) as the gate oxide and an oxygen implant isolation technique. Growth of the device structure including the deposition of Ga2O3(Gd2O3) was performed in a multichamber molecular beam epitaxy system. A 1 μm×100 μm device shows excellent dc and microwave characteristics with low output conductance. Complete pinchoff at Vg=−2.5 V and operation in the accumulation mode of up to Vg=2.5 V were measured. The maximum transconductance was 100 mS/mm, with a high drain current density of 315 mA/mm. Microwave testing yielded a fT of 14 GHz and a fmax of 35 GHz.