Fabrication of Metal–Oxide–Diamond Field-Effect Transistors with Submicron-Sized Gate Length on Boron-Doped (111) H-Terminated Surfaces Using Electron Beam Evaporated SiO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

A H-terminated surface conductive layer of B-doped diamond on a (111) surface was used to fabricate a metal–oxide–semiconductor field-effect transistor (MOSFET) using an electron beam evaporated SiO₂ or Al₂O₃ gate insulator and a Cu-metal stacked gate. When the bulk carrier concentration was approximately 10¹⁵/cm³ and the B-doped diamond layer was 1.5 μm thick, the surface carrier mobility of the H-terminated surface on the (111) diamond before FET processing was 35 cm²/Vs and the surface carrier concentration was 1.5 × 10¹³/cm². For the SiO₂ gate (0.76 μm long and 50 μm wide), the maximum measured drain current at a gate voltage of −3.0 V was −75 mA/mm and the maximum transconductance was 24 mS/mm, and for the Al₂O₃ gate (0.64 μm long and 50 μm wide), these features were −86 mA/mm and 15 mS/mm, respectively. These values are among the highest reported direct-current (DC) characteristics for a diamond homoepitaxial (111) MOSFET.     

Photoluminescence and interface abruptness in InGaAsP/InGaAsP quantum wells

Quantum well (QW) structures consisting of InGaAsP wells and InGaAsP barriers grown by gas-source molecular beam epitaxy have been examined by low temperature photoluminescence (PL) in order to evaluate the contributions of compositional fluctuations in the quaternary alloy and of interface roughness to the PL linewidth. The well material was InGaAsP with a bandgap corresponding to a wavelength of 1.3 μm and the barrier material was InGaAsP of 1.15 μm. The theory for QW excitonic linewidths as a function of well thickness L_z due to fluctuations in alloy composition has been extended to include the case of the quaternary InGaAsP barrier. If the interfaces are atomically abrupt, the linewidth is dominated by compositional fluctuations in the well at large L_z and compositional fluctuations in the barrier at small L_z. The theory predicts a weak dependence of the linewidth on L_z since the composition of the well and barrier are similar. For rough heterointerfaces, the theory indicates the usual increase in linewidth with decreasing L_z. Photoluminescence measurements at 13K in arrays of single InGaAsP/InGaAsP QWs with L_z from 1.0 to 6.0 nm show only a weak variation of the full width at half maximum (FWHM) with L_z, in agreement with the theory for smooth interfaces. Furthermore, the lowest measured FWHM of 8.9 meV was found for a narrow well of L_z=1.8 nm, indicating the InGaAsP/InGaAsP interfaces are smooth and that the PL linewidth is dominated by compositional fluctuations.     

High indium content graded channel GainAs/AlinAs pseudomorphic MODFETs

We report on the electrical and microstructural properties of InP/Ga_xIn ₁ -xAs/Al_0.48In_0.52As modulation doped layers having compositionally graded active channels with different channel thicknesses. The layers were grown by solid source molecular beam epitaxy on Fe-doped InP substrates. The undoped GaInAs two dimensional electron gas channel layers were grown having indium compositions graded fromx = 0.53 at the substrate buffer tox= 0.65 at the heterointerface by varying the Ga cell temperature during growth. Active channel thicknesses of 20 nm and 30 nm were compared with lattice matched layers. Transmission electron microscope image analysis indicates no misfit dislocations in these structures. Hall-effect measurements at 300 K show an increase in the mobility from 8,380 cm²/Vs for the lattice matched layer to 12,500 cm²/Vs for the 30 nm pseudomorphic layer. Small gate-length, 0.25 μn, MODFETs were fabricated to determine effective velocity values from transconductance (g _m ) and current gain (h ₂₁ ) measurements. The peak dc extrinsicg _m increased from 367 mS/mm for the lattice matched layer to 668 mS/mm for the 30 nm pseudomorphic layer. The effective electron carrier velocity increased from 1.57 × 10⁷ cm/s for the lattice matched layer to 1.88 × 10⁷ cm/s for the 30 nm pseudomorphic layer. Our results show that compositional grading is a useful technique to obtain thick pseudomorphic layers with good transport properties.     

Intermetallic Reaction of Indium and Silver in an Electroplating Process

The reaction of indium (In) and silver (Ag) during the electroplating process of indium over a thick silver layer was investigated. It was found that the plated In atoms react with Ag to form AgIn₂ intermetallic compounds at room temperature. Indium is commonly used in the electronics industry to bond delicate devices due to its low yield strength and low melting temperature. In this study, copper (Cu) substrates were electroplated with a 60-μm-thick Ag layer, followed by electroplating an In layer with a thickness of 5 μm or 10 μm, at room temperature. To investigate the chemical reaction between In and Ag, the microstructure and composition on the surface and the cross section of samples were observed by scanning electron microscopy (SEM) with energy-dispersive x-ray spectroscopy (EDX). The x-ray diffraction method (XRD) was also employed for phase identification. It was clear that indium atoms reacted with underlying Ag to form AgIn₂ during the plating process. After the sample was stored at room temperature in air for 1 day, AgIn₂ grew to 5 μm in thickness. With longer storage time, AgIn₂ continued to grow until all indium atoms were consumed. The indium layer, thus, disappeared and could barely be detected by XRD. Jong S. Kim now with Applied Materials.     

Growth of device quality GaAs by chemical beam epitaxy

The growth of high purity GaAS with excellent uniformity and very low defect density by chemical beam epitaxy using triethylgallium and arsine is described. The residual background impurity is mostly carbon. A mobility of 518 cm²/Vs with a hole density of 3.6 x 10¹⁴ cm⁻³ has been obtained for a growth temperature of 500° C. The electrical quality is further evaluated by fabricating a Si doped epilayer into MESFET device using 1 μm gate length. A transconductance of 177 mS/mm has been measured. The results indicate that chemical beam epitaxy is a very attractive growth technique for GaAs integrated circuits.     

Minimization of leakage current of recessed gate AlGaN/GaN HEMTs by optimizing the dry-etching process

The backward current of Schottky contacts on unintentionally doped GaN samples prepared by different dry-etching methods was investigated. It was found that an ion beam etching (IBE) process with an accelerating voltage of 250 V under an angle of 20 degrees to minimize channeling achieves the best results. The backward current in this case is 4 × 10⁻¹⁰ A/μm² compared to the backward current of the unetched sample of 1 × 10⁻⁷ A/μm² at −100 V. With this process, recessed gate HEMTs on AlGaN/GaN heterostructures grown by low pressure MOVPE were fabricated and compared to HEMTs without recess. The applied gate recess etching technique improves the leakage current by nearly a factor of two. The maximum transconductance is improved from 40 mS/mm to 60 mS/mm at a gate length of 4 μm.     

Absorptivity of semiconductors used in the production of solar cell panels

The dependence of the absorptivity of semiconductors on the thickness of the absorbing layer is studied for crystalline silicon (c-Si), amorphous silicon (a-Si), cadmium telluride (CdTe), copper indium diselenide (CuInSe₂, CIS), and copper gallium diselenide (CuGaSe₂, CGS). The calculations are performed with consideration for the spectral distribution of AM1.5 standard solar radiation and the absorption coefficients of the materials. It is shown that, in the region of wavelengths λ = λ _g = hc/E _g , almost total absorption of the photons in AM1.5 solar radiation is attained in c-Si at the thickness d = 7−8 mm, in a-Si at d = 30–60 μm, in CdTe at d = 20−30 μm, and in CIS and CGS at d = 3−4 μm. The results differ from previously reported data for these materials (especially for c-Si). In previous publications, the thickness needed for the semiconductor to absorb solar radiation completely was identified with the effective light penetration depth at a certain wavelength in the region of fundamental absorption for the semiconductor.     

Dependence of photoluminescence spectra of epitaxial Pb1 ? xEuxTe (0 ≤ x ≤ 0.1) alloy layers on conditions of growth

The photoluminescence spectra of the Pb_{1 − x} Eu _x Te (0 ≤ x ≤ 0.1) alloy are studied at low temperatures. Epitaxial layers were grown by molecular-beam epitaxy at different temperatures. Along with the basic line corresponding to interband radiative recombination, additional emission lines are observed in the low-energy region of the spectra. Some nonuniformities are observed at the sample surface (within an area smaller than 1% of the total surface area). The concentration and size (1–10 μm) of the nonuniformities decrease with increasing temperature of growth. The additional emission lines are attributed to local nonuniformities in the layer. The dependence of the band gap of the Pb_1−x Eu _x Te (0 ≤ x ≤ 0.1) alloy on the composition parameter x is determined at 77.4 K. The dependence is nonlinear and adequately described by the relation E _g [eV] = 0.213 + 4.8x − 18.4x ².     

Epitaxial Lead Chalcogenides on Si for Mid-IR Detectors and Emitters Including Cavities

Lead chalcogenide (IV–VI narrow-gap semiconductor) layers on Si or BaF₂(111) substrates are employed to realize two mid-infrared optoelectronic devices for the first time. A tunable resonant cavity enhanced detector is realized by employing a movable mirror. Tuning is across the 4 μm to 5.5 μm wavelength range, and linewidth is <0.1 μm. Due to the thin (0.3 μm) PbTe photodiode inside the cavity, a higher sensitivity at higher operating temperatures was achieved as compared to conventional thick photodiodes. The second device is an optically pumped vertical external-cavity surface-emitting laser with PbTe-based gain layers. It emits at ∼5 μm wavelength and with output power up to 50 mW pulsed, or 3 mW continuous wave at 100 K.     

DESIGN AND FABRICATION OF Si/SiGe PMOSFETs

Based on theoretical analysis and computer-aided simulation, optimized design prin-ciples for Si/SiGe PMOSFET are given in this paper, which include choice of gate materials, determination of germanium percentage and profile in SiGe channel, optimization of thickness of dioxide and silicon cap layer, and adjustment of threshold voltage.In the light of these principles, a SiGe PMOSFET is designed and fabricated successfully.Measurement indicates that the SiGe PMOSFET‘s(L=2μ同洒45 mS/mm(300K) and 92 mS/mm(77K) ,while that is 33mS/mm (300K) and 39mS/mm (77K) in Si PMOSFET with the same structure.     

Vapor growth of InP for MESFET’S

Epitaxial layers of InP have been grown by the conventional In/PCl₃/H{ion2} technique. With the aim of fabricating FET’s structures, we have studied the growth of low doped buffer layers and the doping by H₂S. It has been shown, that the purity of the layers increases from experiment to experiment and that low doped layers, in the 10¹³ – 10¹⁴ cm^-3 range, are obtained after growth of about 10 layers. Evidence for the purity of these layers have been obtained from Hall, photoluminescence and SIMS measurements. Cr and Fe outdiffusion from the substrate has been studied by SIMS. Fe is found to diffuse from the substrates, even in the case of substrates which are not intentionally doped with Fe. Some FET’s have been fabricated on epitaxial structures with and without buffer layers: the static characteristics of the transistors are encouraging (I_Dss = 24 mA, g_m = 19 mS for a gate of 2 μm and 200 μm in length and width, respectively); the pinch-off is better in devices fabricated from structures with buffer layers.     

OMVPE growth of InP and Ga0.47ln0.53as using ethyldimethylindium

We report the organometallic vapor phase epitaxial (OMVPE) growth of InP and Ga_0.47In_0.53As using a new organometallic indium source, ethyldimethylindium (EDMIn), rather than the traditional sources triethylindium (TEIn) or trimethylindium (TMIn). EDMIn is a liquid at room temperature and its vapor pressure at 17° C was found to be 0.85 Torr using thermal decomposition experiments. The growth results using EDMIn were compared to those using TMIn in the same atmospheric pressure reactor. For InP, use of EDMIn resulted in a high growth efficiency of 1.3 × 10⁴ μm/ mole, which was independent of the growth temperature and comparable to the growth efficiency obtained with TMIn. The high growth efficiency is consistent with the observation of no visible parasitic gas phase reactions upstream of the substrate. The 4K photoluminescence (PL) spectra consist of a peak due to bound excitons and an impurity related peak 38 meV lower in energy. This impurity peak is ascribed to conduction band to acceptor transitions from carbon, due to the decreasing relative intensity of this peak with increasing V/III ratio. The relative intensity of the C impurity peak decreases by five times when the growth temperature is increased from 575 to 675° C, with a corresponding increase in the room temperature electron mobility from 725 to 3875 cm²/ Vs. For GalnAs lattice-matched to InP, use of EDMIn also resulted in a temperatureindependent high growth efficiency of 1.0 x 10⁴ μm/mole, indicating negligible parasitic reactions with AsH₃. The In distribution coefficient was nearly constant at a value of 0.9, however the run to run composition variation was slightly higher for EDMIn than for TMIn. The 4K PL showed donor-acceptor pair transitions due to C and Zn. The C impurity peak intensity decreased dramatically with increasing growth temperature, accompanied by an increase in the room temperature electron mobility to 5200 cm²/Vs. Overall, the growth of both InP and GalnAs using EDMIn was qualitatively similar to that using TMIn, although the room temperature electron mobilities were lower for the new source than for our highest purity bottle of TMIn.     

Resonant-cavity infrared optoelectronic devices

The Cd_xHg_1−xTe compounds are well suited to the design of resonant microcavity devices. Indeed these compounds display a wide variation of bandgap and refractive index with composition, while the lattice parameter remains practically unchanged. Microcavities resonating in the 3–5 μm range have been prepared by molecular beam epitaxy. Light emitting diodes (LEDs) are obtained by stacking a lower Bragg mirror (10.5 periods) which is doped n-type and a nominally undoped cavity medium containing a 50 nm active layer (CdTe-HgTe pseudo-alloy). The upper mirror is a gold layer deposited on the cavity, which is partly p-type doped. The diode emission is observed under direct bias, up to room temperature, in coincidence with the cavity resonance mode (linewidth 8 meV). It is much narrower than the inhomogeneous linewidth of the active layer (60 meV at 300K). The directivity is also much better. The diode properties are only very slightly dependent on temperature. A similar device can also be designed to make an infrared detector whose active layer thickness is reduced with respect to conventional detectors. The detector efficiency at the resonance wavelength may be increased by a factor close to the cavity finesse. With 16.5 periods in the lower mirror and a dielectric mirror as upper mirror (seven periods of ZnS/YF₃), it has been possible to make a cavity resonating at 3.06 μm whose quality factor reaches 350. By photopumping the cavity across the dielectric mirror with a YAG microlaser, a laser emission occurred at the cavity resonance. At 10K, the laser threshold is 45 kW/cm₂ and the linewidth is only 1.7 meV. These results demonstrate the usefulness of the microcavity concept for designing new devices such as LED or lasers which could be the basis for new applications of CdHgTe compounds.     

Molecular beam epitaxy of in1-xGaxASyP1-y(y ≃2.2 ×) lattice matched to InP using gas cells

In this paper we report MBE growth of quaternary alloys In_1-xGa_xAs_yP_1-y (y≃2.2x, 0 <y < 1) lattice matched to InP, by using gas cells as sources of V elements. The growth is performed in a MBE system which can receive both gas and solid cells. An efficient pumping system made from association of cryo and turbo molecular pumps allows a background hydrogen pressure of ≃ 10^-5 Torr during the growth. Gas sources produce P₂ and As₂ flux from cracking of PH₃ and AsH₃. An accurate and flexible control of P₂ and As₂ flux is obtained by monitoring the gas cells by a mass selector system. Electron probe analysis and X-ray diffraction show that reproducible growth of homogeneous quaternary layers with a precise control of the composition can be achieved with gas cells. Possible contamination by residual impurities coming from the cracking furnace is investigated by low temperature photoluminescence (8 K). Typical spectrum (8 K) exhibits a narrow near band edge peak (FWHM = 17 meV) and a secondary peak located at 14 meV below the first one which is attributed to carbon acceptor impurity. Room temperature photoluminescence efficiency is equal to that obtained by LPE. For In_0.60Ga_0.40As_0.90Po_0.10 background carrier concentration isn = 10¹⁶cm^-3 with electron mobilities μ (300 K) = 6000 cm²/Vsec and μ (77 K) = 13000 cm²/Vsec.     

High-transconductance p-channel InGaAs/AlGaAs modulation-doped field effect transistors

A p-channel quantum-well InGaAs/AlGaAs modulation-doped field effect transistor has been fabricated. With a 1-µm gate, the device exhibits transconductances of 17.8 and 89 mS/mm at room temperature and 77 K, respectively. Experimental results indicate an extrinsic transconductance greater than 200 mS/mm is achievable with reduced ohmic contact resistance and gate leakage.     

Drain current enhancement and negligible current collapse in GaN MOSFETs with atomic-layer-deposited HfO2 as a gate dielectric

Accumulation-type GaN metal-oxide-semiconductor field-effect-transistors (MOSFET’s) with atomic-layer-deposited HfO₂ gate dielectrics have been fabricated; a 4 μm gate-length device with a gate dielectric of 14.8 nm in thickness (an equivalent SiO₂ thickness of 3.8 nm) gave a drain current of 230 mA/mm and a broad maximum transconductance of 31 mS/mm. Owing to a low interfacial density of states (D_it) at the HfO₂/GaN interface, more than two third of the drain currents come from accumulation, in contrast to those of Schottky-gate GaN devices. The device also showed negligible current collapse in a wide range of bias voltages, again due to the low D_it, which effectively passivate the surface states located in the gate-drain access region. Moreover, the device demonstrated a larger forward gate bias of +6 V with a much lower gate leakage current.     

Systematic optical and x-ray study of In x Ga1−x As on InP

We present a systematic study of In _x Ga_1−x As on InP grown by molecular beam epitaxy using the characterization techniques of Fourier transform photoluminescence, x-ray diffraction, micro-Raman spectroscopy, and photoreflectance spectroscopy. The four techniques were used to determine and correlate the fundamental parameters of band-gap energy, phonon frequency and composition. Comparing room temperature (293 K) PL and low temperature PL indicate the presence of a partially ionized acceptor with binding energy of about 13 meV in the unintentionally doped material. Double crystal x-ray diffraction (XRD) using a symmetric <400> and asymmetric <224> reflections was also employed. The use of two reflections gives precise lattice constants, composition, and extent of film relaxation. Micro-Raman spectroscopy was used to measure phonon frequencies in the In _x Ga_1−x As films and correlated to XRD composition. Room temperature photoreflectance (PR) was used to determine band-gap energy for both the low and intermediate field cases. Band gap energies determined at room temperature by PL and PR were in agreement within experimental error.     

Origin of photoluminescence from Er3+ centers in erbium doped GaAs and Al0.4Ga0.6 As grown by MBE

Sharp erbium-related intra-4f shell luminescence from Er doped GaAs and Al_0.4Ga_0.6 As epitaxial layers grown by molecular beam epitaxy (MBE) is presented. The emission arising from the two Er³⁺ excited states,⁴I_13/2 and⁴I_11/2 are studied. We have observed, by means of heat treatment under differentambients such as As, Ga and Al over pressure, that the optically active Er³⁺ preferentially occupies a Column III lattice site or Column III related defects. The photoluminescence results of co-doping Al_0.4Ga_0.6As:Er with Si and Be by MBE is also reported for the first time. A strong single 1.54 μm spontaneous emission line is achieved by co-doping with Be (≈1×10¹⁸ cm⁻³). This improvement is a result of successfully eliminating or suppressing the other transitions without sacrificing the 1.54 μm emission intensity or linewidth.     

A Low-Voltage Low-Power Rail-to-Rail Constant g m Transconductance Amplifier

In this paper, a low-voltage low-power rail-to-rail constant g _m transconductance amplifier (TA) is introduced. The supply voltages are set at (±1.5 V). The circuit depends on selecting the maximum transconductance (g _m ) to achieve an almost constant g _m over the entire common-mode (CM) range. The circuit is then used to realize a second-order 4 MHz lowpass filter consuming 530 W, and a fifth-order 450 kHz lowpass elliptic filter consuming 2.3 mW. Both filters can be integrated on silicon without any external connections.     

Properties of highly conducting nitrogen-plasma-doped ZnSe:N thin films

Values for the acceptor ionization energy, E_a, and compensating donor ionization energy, E_d, have been obtained from an analysis of variable-temperature photoluminescence data taken for a series of highly conducting nitrogen-plasma doped ZnSe thin films. E_awas found to be highly temperature dependent, with values ranging from E_a ~110 meV at low temperatures to ~60 meV at room temperature. The compensating donor ionization energy ranged from E_d ~31 meV at low temperatures to ~24 meVat room temperature. These results provide clear evidence of thenonhydrogenic nature of the nitrogen acceptor state in heavily doped ZnSe:N thin films and suggest that interstitial bonding of N, at two or more stable sites, may play a central role in the p-type doping and compensation of this material at high doping levels.