N. Pan

Observation of a two‐dimensional electron gas in low pressure metalorganic chemical vapor deposited GaN‐AlxGa1−xN heterojunctions

We have confirmed the presence of a two‐dimensional electron gas (2DEG) in a wide band‐gap GaN‐AlxGa1−xN heterojunction by observing steplike features in the quantum Hall effect. The 2DEG mobility for a GaN‐Al0.13Ga0.87N heterojunction was measured to be 834 cm2/V s at room temperature. It monotonically increased and saturated at a value of 2626 cm2/V s at 77 K. The 2DEG mobility remained nearly constant for temperatures ranging from 77 to 4.2 K. Using Shubnikov–de Haas (SdH) measurements the two‐dimensional carrier concentration was estimated to be 1×1011 cm−2. The peak mobility for the 2DEG was found to decrease with the heterojunction aluminum compositions in excess of 13%.

Photoreflectance characterization of AlGaAs/GaAs modulation‐doped heterostructures

Photoreflectance (PR) and reflectance have been applied to characterize undoped and modulation‐doped heterostructures of AlGaAs/GaAs grown by metal‐organic chemical vapor deposition. The PR spectra were taken on these samples after sequential etching steps in a phosphoric acid etch to study the effects of the surface electric field, the heterointerface, and the two‐dimensional electron gas. PR spectra were also taken with an external electric field applied through a transparent gate electrode. The results show that the oscillations appearing near the bandgap energy of GaAs are Franz–Keldysh oscillations originating from the large surface electric field. The surface electric field of the heterostructures can be modified through the application of an external electric field or by etching. The oscillation period is observed to increase with increasing reverse bias or with etching of the GaAs cap layer and the PR features disappear at a forward bias of 0.45 V. The very sharp features associated with the GaAs ...

Si delta‐doped field‐effect transistors by atmospheric pressure metalorganic chemical vapor deposition

Si delta‐doped GaAs field‐effect transistors (FETs) are demonstrated by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) and characterized by Hall‐effect, capacitance‐voltage (C‐V), and Shubnikov de‐Haas measurements. The Si delta doping was accomplished by interrupting the growth and flowing silane with controlled timing under an arsenic overpressure. Devices with 0.5 μm gate length (Ns=2.2×1012 cm−2) were fabricated with a maximum extrinsic transconductance of 140 mS/mm and a current gain cutoff frequency of 17 GHz. The transconductance as a function of gate voltage showed a plateau region through a range of 1.5 V further supporting spatial confinement of the electrons.

Low temperature InAlAs buffer layers using trimethylarsenic and arsine by metalorganic chemical vapor deposition

Low temperature (LT) InAlAs buffer layers grown lattice matched to InP substrates using a combination of trimethylarsenic and arsine were demonstrated. The LT InAlAs buffer layer showed excellent surface morphology with a maximum resistivity of 2×105 Ω cm at a growth temperature of 475 °C. Low temperature photoluminescence and Hall‐effect measurements confirming the high quality of epitaxial layers grown on top of the LT InAlAs buffer layer. Electrochemical capacitance voltage measurements consistently confirmed the absence of conductive impurity spikes at the epitaxial/substrate interface.

Atomic layer epitaxy of InP using trimethylindium and tertiarybutylphosphine

Abstract Atomic layer epitaxy (ALE) growth of InP was investigated using trimethylindium (TMI) and tertiarybutylphosphine (TBP) in a horizontal atmospheric reactor. The studied growth parameters were exposure times, TMI and TBP fluxes, and growth temperature. Self-limiting ALE growth of InP was achieved at a growth temperature of 340°C. Substantial increases in the TMI flux and higher growth temperatures exceeding 340°C resulted in growth rates exceeding 1 monolayer per cycle. Uniform ALE InP layers were verified by cross-sectional transmission electron micrography and sputtered Auger profiling. The application of thin ALE InP layers (15 A) on GaAs surfaces was investigated using X-ray photoelectron spectroscopy, 77 K photoluminescence, and 300 K photoreflectance. The absence of arsenic oxide and an increase in the photoluminescence intensity by a factor of 2 were observed after InP passivation.

Be doped GaAs grown by migration enhanced epitaxy at low substrate temperature

Conductive Be doped GaAs grown by molecular beam epitaxy at low substrate temperatures (300° C) was obtained for the first time by using migration enhanced epitaxy (MEE) without subsequent annealing. The layers were characterized using Hall effect, double crystal x-ray diffraction, and photoluminescence. With low arsenic exposure, the low temperature MEE layers doped with Be had the same carrier density and similar luminescent efficiency as layers grown by conventional MBE at 580° C. Mobility at 77 K was reduced somewhat for layers doped at 2 × 1017cm−3, which also exhibited hopping conductivity below 40 K. Double crystal x-ray diffraction showed that low temperature MEE samples grown at low As exposure had the narrow linewidth associated with conventional MBE material grown at 580° C, unlike layers grown by conventional MBE at low temperatures, which exhibit an expansion in lattice parameter.

Growth of pseudomorphic high electron mobility heterostructures by atmospheric pressure metalorganic chemical vapor deposition

Inverted pseudomorphic high electron mobility transistor (HEMT) and inverted HEMT heterostructures are demonstrated by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) for the first time and characterized by transmission electron microscopy (TEM), variable temperature Hall effect, and Shubnikov–de Haas measurements. TEM micrographs of both structures show distinct and sharp heterojunction interfaces without indications of interface roughness at the AlGaAs/channel layer interface. Variable temperature Hall effect measurements reveal a monotonic increase in mobility as the temperature is lowered. For the inverted HEMT, the mobility at 15 K is 90 000 cm2/V s with a sheet density of 8.2×1011 cm−2. The mobility of the inverted pseudomorphic HEMT at 15 K is 73 000 cm2/V s with a sheet density of 1.5×1012 cm−2. Shubnikov–de Haas measurements at 4.2 K in magnetic fields up to 18.5 T show clear magnetoresistance oscillations and plateaus in the quantum Hall effect confirming the existence of a t...

Graded InGaP schottky diodes on Si-doped InP

A compositionally graded InGaP alloy layer grown on a Si‐doped InP layer was used to enhance the Schottky barrier height of InP. The fabricated diodes were characterized by Auger depth profiling, variable temperature I‐V, capacitance‐voltage (C‐V), and internal photoemission. Rectification behavior with a low leakage current was achieved (J=8.3×10−7 A/cm2 at −1V). An enhanced Schottky barrier height of 1.18 eV was measured. The large barrier height permitted a reliable C‐V profile of a moderately doped InP layer (7×1017 cm−3).

InAlAs/InP modulation doped heterostructures by atmospheric pressure metalorganic chemical vapor deposition using tertiarybutylphosphine

Undoped and modulation doped InAlAs/InP heterostructures with excellent optical and electrical characteristics are demonstrated using tertiarybutylphosphine (TBP). Low‐temperature photoluminescence spectra showed the presence of a type II interface transition indicating the high quality of the interface. Two‐dimensional electron gas transport in a modulation doped sample containing a sheet density of 1.8×1012 cm−2 was verified by observing plateaus in the quantum Hall effect. These results confirmed that TBP can be substituted for phosphine for the growth of high quality InAlAs/InP heterostructures.

Optimization of buffer layers for AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors by atmospheric pressure metalorganic chemical vapor deposition

Pseudomorphic AlGaAs/InGaAs/GaAs high electron mobility transistors (HEMT) incorporating various types of buffer layers were fabricated (D = 0.50 × 100μm) and characterized by Hall-effect measurements, low temperature photoluminescence (PL), and room temperature IV characteristics. The devices fabricated with a thick (5000Å) undoped high purity GaAs buffer layer grown at 650° C showed poor pinch-off characteristics, high output conductance and large leakage currents (>2 mA at pinch-off). Devices incorporating an undoped high purity GaAs (3000Å) buffer layer grown at 550° C showed sharp pinch-off characteristics, low output conductance, and low leakage currents (1.3 mA at pinch-off). Low temperature growth of GaAs (550° C) enhanced carbon incorporation resulting in increasedp-type characteristics. This type of buffer layer provided additional barrier height between the active layer and the substrate reducing the injection of electrons into the substrate.