Nonalloyed ohmic contacts to n-type GaAs by pulsed ruby laser diffused tin from tin-silica film

Nonalloyed ohmic contacts were formed on n⁺diffused layers on GaAs. The n⁺layers were formed on semi-insulating substrates by depositing a layer of tin-silica film and irradiating by ruby laser alone without thermal diffusion. Vacuum-evaporated AuGe-Ni contacts display low specific contact resistance ≃1.8 × 10^-6Ω.cm², without alloying.     

Self-aligned GaAs MISFET's with a low-temperature-grown GaAs gateinsulator

GaAs MISFET's with a low-temperature-grown (LTG) GaAs gate insulator and ion-implanted self-aligned source and drain n⁺ regions are demonstrated. The resistivity and breakdown field of the LTG GaAs insulator were not changed appreciably by implantation and 800°C activation annealing. The gate leakage current remained very low at a value of approximately 1 μA per μm² of gate area at 3 V forward gate bias. Because of the reduced source and drain resistance, the drain saturation current and the transconductance of self-aligned MISFET's increased more than twofold after ion implantation     

Characteristics of siliconn+-n--n+ diode with sub-micrometer n- region

In this paper, the I-V characteristics of silicon n⁺-n ^--n⁺ diode are investigated as a parameter of the length of the n^- region. This diode with shorter n^- region than 1 μm has the ohmic characteristics until reaching high electric field in spite of the existence of numerous space-charges in the n^- region, for the first time in this report. This conductance of the diode is inversely proportional to the third power of the length of the n^- region. The experimental results are in good agreement with an analytical calculation including the diffusion term of carriers injected from the n+ regions to the n^- region. However, the diode with longer n^- region than 2 μm shows the space-charge-limited conduction which is the same as earlier reports     

A bipolar mechanism for alpha-particle-induced soft errors in GaAsintegrated circuits

The alpha-particle-induced collected charge in undoped LEC semi-insulating GaAs is measured in n⁺-i-n⁺ and n ⁺-p-n⁺ isolation structures and is compared with the results of an analytical model based on a bipolar mechanism. In n ⁺-i-n⁺ isolation structures, a collected-storage multiplication phenomenon induced by alpha-particle incidence is observed. The measured collected charge is about three times the alpha-particle-generated charge. This phenomenon can be attributed to charge transfer between two adjacent n⁺ regions. The dominant charge-collection process continues for 2.4 ns in n⁺-i-n⁺ isolation structures, but in n⁺-p-n⁺ isolation structures, it stops within 0.8 ns. The measured collected charge decreases as the isolation gap and background acceptor concentration increase. These experimental results can be explained semiquantitatively by the analytical model. This suggests that the primary mechanism of soft errors in GaAs ICs is a bipolar mechanism     

High-performance InGaAs junction field-effect transistor with P/Beco-implanted gate

InGaAs junction field-effect transistors (JFETs) are fabricated in metalorganic chemical-vapor-deposition (MOCVD)-grown n-InGaAs and semi-insulating Fe:InP layers on n⁺-InP substrate with a P/Be co-implanted p⁺ self-aligned gate. The device exhibits a transconductance of 245 mS/mm (intrinsic transconductance of 275 mS/mm) at zero gate bias and good pinch-off behavior for a gate length of 0.5 μm. The effective electron velocity is deduced to be 2.8×10⁷ cm/s, equal to the theoretical prediction     

Carrier distribution and low-field resistance in short n+-n--n+and n+-p--n+structures

In the present paper, we calculate the potential, field, and carrier distributions in short n⁺-n^--n⁺and n⁺-p^--n⁺devices and estimate the low-field resistance. The results of the calculations present a set of universal curves which may be used to find the minimum carrier density in the sample, the barrier height, the electric field at the boundary, etc. Our calculations show that electron injection becomes very important when the doping level is smaller than 1.5 × 10¹⁴(cm^-3). (T/300 K)/ L²(µm) for GaAs diodes, whereLis the sample length. The low-field resistance of the sample is limited by the thermionic emission of the sample and by the diffusion and drift in the sample. The thermionic emission dominates at low temperatures, in short samples, and the diffusion-drift dominates in longer samples at higher temperatures. The experimental values of low-field resistance for GaAs 0.4-µm n⁺-n^--n⁺devices at 77 and 300 K are in good agreement with the predicted values. The agreement is not so good for 0.25-µm devices and for n⁺-p^--n⁺devices. In the latter case, the disagreement may be due to uncertainty in the doping level because the low-field resistance of the n⁺-p^--n⁺structure is shown to be very sensitive to the doping level of the p-region.     

High speed III-V electrooptic waveguide modulators at λ-1.3μm

Traveling wave GaAs electrooptic waveguide modulators at a wavelength of 1.3 μm with bandwidth in excess of 20 GHz have been developed and characterized. The design and characteristics of both p-i-n modulators in microstrip configuration and Schottky barrier on n ^--GaAs/semi-insulating (SI) GaAs in the coplanar strip configuration modulators are discussed. It is shown that microwave loss and slowing on n⁺ GaAs substrates will limit the bandwidth of the microstrip modulator to less than 10 GHz for a device 8 mm in length. Modulators with bandwidths in excess of 10 GHz are fabricated on SI GaAs substrates     

A novel MESFET fabricated by a simple internal interconnectiontechnique

A new type of internal interconnection of devices has been developed by implanting a buried horizontal n⁺ layer and vertical n⁺ columns inside semi-insulating GaAs. Based on this technique, a novel MESFET with small intrinsic gate-source resistance has been fabricated and tested     

MOVPE-grown millimeter-wave InGaAs mixer diode technology andcharacteristics

The merits of InGaAs-based millimeter-wave mixer diodes are explored experimentally and theoretically. Schottky junctions on InGaAs exhibit barriers (φ_b) in the neighborhood of 0.25 eV. The high mobility of InGaAs contributes to the low n⁺ sheet resistances of 1.9-5 Ω/square for 1-μm n⁺ InGaAs layers (n_s=1.5×10¹⁹ cm^-3, μ _n=1800 cm²/V·s) grown with our in-house Metalorganic Vapor Phase Epitaxy (MOVPE) system, The design, material growth, fabrication, and characterization of InGaAs integrated mixer/antennae are reported. Pt plating technology, adapted here for InGaAs Schottky contacts, has improved the ideality factor (η) and yield relative to conventional evaporated Pt. With 810 μW of local oscillator power, applied to the diode, and zero DC bias, an integrated InGaAs mixer/antenna demonstrated an excellent diode performance of 199 K RF input double-sideband noise temperature with a corresponding single-sideband (SSB) conversion loss (L_c) of 5.0 dB at LO, RF, and IF frequencies of 94 GHz, 94 GHz±1.4 GHz, and 1.4 GHz, respectively. Likewise, the diodes in an InGaAs subharmonic integrated mixer/antenna demonstrated an equivalent RF-port double-sideband (DSB) noise temperature (T_mix) of 1058 K and single-sideband conversion loss of 10.2 dB at 180 GHz with a 90-GHz LO power (PLO) of 1.6 mW. Compared to GaAs diodes with RF coupling and IF losses removed, the single-ended InGaAs noise temperature results were within 46-100 K of those for state-of-the-art GaAs mixer diodes while requiring significantly less LO power     

Use of Sn-doped GaAs for non-alloyed ohmic contacts to HEMTs

Segregation of Sn to the surface of MBE grown n⁺-GaAs layers allows fabrication of non-alloyed Ti/Pt/Au, Al or Ti/W ohmic contacts with low specific contact resistivities (1.1×10^-6 Ω·cm^-2). These contacts were used to realise high performance HEMTs (g_m=230 mS/mm for 1.0 μm gate length) in which Si is used as the dopant in the donor AlGaAs layer and Sn is employed in the GaAs contact layer     

Influence of Al content x on hot electron noise in AlxGa1-xAs n+nn+ devices: comparison withGaAs

Hot electron noise measurements are performed in Si doped Al_x Ga_1-xAs n⁺nn⁺ devices, for three different Al concentrations: x=0.15, 0.2, 0.25. Noise temperatures are obtained using a pulsed measurement technique as functions of electric field and frequency. Longitudinal diffusion coefficients D(E) are deduced at 4 GHz. Results are analyzed through the scattering mechanisms which greatly affect the electron velocity properties of Al_xGa_1-xAs materials. Comparisons with n⁺ nn⁺ GaAs devices are made     

Alpha-particle-induced charge collection in p-n junction diodes insemi-insulating GaAs substrates

The bias and angle dependences of the alpha-particle-induced charge collected by GaAs p-n junction diodes are investigated. These diodes, in which the n-layer overlays the p-layer, are fabricated in a semi-insulating GaAs substrate by Si and Mg ion implantation. ²⁴¹ Am placed in a vacuum is used as an alpha-particle source with an initial energy of 4.03 MeV and a fluence of 5.4×10^-5/s/μm². The results show that the collected charge is nearly independent of the applied bias. This bias independence may be further evidence that the charge funneling process is not important in semi-insulating GaAs. A model not incorporating funneling can explain the measured angular dependence. Based on this model, the design principle for the buried p-layer structure is discussed     

Diffusion and noise in GaAs material and devices

The variation of the diffusion coefficient D(E) versus the electric field strength E is determined at 300 K in n-type GaAs (N_D=3×10^-17 cm^-3 ), using pulsed high-frequency noise measurements. D(E) is found to increase slightly at low field, then to decrease down to one tenth of its ohmic value near the threshold field. Long (⩾4 μm) real n⁺-n-n⁺ Gunn diodes, with an arbitrary doping profile, can be modeled. Comparisons are made, and excellent agreement is found, between experimental and theoretical characteristics of two real diodes, with notch and with gradual doping profiles. The doping profile N_D(x ) is shown to have a considerable influence on the diode behavior, in regard to the electric field profile as well as the noise characteristics. Using the impedance field method, the noise current is modeled and found to by very sensitive in the D(E) variation law, in particular in the range of 2.5-4 kV/cm. The agreement between the experimental noise and the computed noise of real diodes is quite satisfactory when using the D(E) determined     

Characterization of double pulse-doped channel GaAs MESFETs

The fabrication and characterization of a double pulse-doped (DPD) GaAs MESFET grown by organometallic vapor phase epitaxy (OMVPE) are reported. The electron mobility of a DPD structure with a carrier concentration of 3×10¹⁸/cm³ was 2000 cm²/V-s, which is about 20% higher than that of a pulse-doped (PD) structure. Implementing the DPD structure instead of the conventional PD structure as a GaAs MESFET channel, the drain breakdown voltage, current gain cutoff frequency, and maximum stable gain (MSG) increase. The maximum transconductance of 265 mS/mm at a drain current density of 600 mA/mm, a current gain cutoff frequency of 40 GHz, and an MSG of 11 dB at 18 GHz were obtained for a 0.3 μm n⁺ self-aligned DPD GaAs MESFET     

Heterojunction blocking contacts in MOCVD grown Hg1-xCdxTe long wavelength infrared photoconductors

The theoretical and experimental performance of Hg_1-xCd _xTe long wavelength infrared (LWIR) photoconductors fabricated on two-layer heterostructures grown by in situ MOCVD has been studied. It is shown that heterojunction blocking contact (HBC) photoconductors, consisting of wider bandgap Hg_1-xCd_x Te on an LWIR absorbing layer, give improved responsivity, particularly at higher applied bias, when compared with two-layer photoconductors incorporating n⁺/n contacts. An extension to existing device models is presented, which takes into account the recombination rate at the heterointerface and separates it from that occurring at both the contact-metal/semiconductor and passivant/semiconductor interfaces. The model requires a numerical solution to the continuity equation, and allows the device responsivity to be calculated as a function of applied electric field. Model predictions indicate that a change in bandgap across the heterointerface corresponding to a compositional change of Δx⩾0.04 essentially eliminates the onset of responsivity saturation due to minority carrier sweepout at high applied bias. Experimental results are presented for frontside-illuminated n-type Hg_1-xCd_xTe photoconductive detectors with either n⁺/n contacts or heterojunction blocking contacts. The devices are fabricated on a two-layer in situ grown MOCVD Hg_1-xCd_xTe wafer with a capping layer of x=0.31 and an LWIR absorbing layer of x=0.22. The experimental data clearly demonstrates the difficulty of forming n ⁺/n blocking contacts on LWIR material, and indicates that heterojunctions are the only viable technology for forming effective blocking contacts to narrow bandgap semiconductors     

A column-base InP lateral bipolar transistor

An InP lateral bipolar transistor has been successfully fabricated on a semi-insulating substrate by implanting Si⁺ as the emitter and collector contacts and Mg⁺ as the column base. An array of 33 1-μm-diameter columns with 1-μm separation between each was formed between the emitter-collector spacing of 3 μm. A current gain of 290 was obtained at 77 K; it was over 12 at room temperature     

A 630-mS/mm GaAs MESFET with Au/WSiN refractory metal gate

GaAs MESFET's with a gate length as low as 0.2 μm have been successfully fabricated with Au/WSiN refractory metal gate n⁺-self-aligned ion-implantation technology. A very thin channel layer with high carrier concentration was realized with 10-keV ion implantation of Si and rapid thermal annealing. Low-energy implantation of the n⁺-contact regions was examined to reduce substrate leakage current. The 0.2-μm gate-length devices exhibited a maximum transconductance of 630 mS/mm and an intrinsic transconductance of 920 mS/mm at a threshold voltage of -0.14 V     

An electrically and optically gate-controlled Schottky/2DEGvaractor

A novel gate-controlled varactor is reported. The three-terminal varactor is a modulation-doped heterostructure of AlGaAs/GaAs with two Schottky contacts directly made to a two-dimensional electron gas (2DEG). The third, gate, contact is formed from highly doped n⁺ GaAs material to allow an open optical window that can be used for optical gating and mixing. Structure capacitance is less than 1 pF and a change of more than 30% from the zero bias capacitance is observed with the applied gate voltage. The capacitance also increases proportionally with applied light and inversely with the terminal voltage     

Low multiplication noise thin Al0.6Ga0.4Asavalanche photodiodes

Avalanche multiplication and excess noise were measured on a series of Al_0.6Ga_0.4As p⁺in⁺ and n⁺ip⁺ diodes, with avalanche region thickness, w ranging from 0.026 μm to 0.85 μm. The results show that the ionization coefficient for electrons is slightly higher than for holes in thick, bulk material. At fixed multiplication values the excess noise factor was found to decrease with decreasing w, irrespective of injected carrier type. Owing to the wide Al_0.6Ga_0.4As bandgap extremely thin devices can sustain very high electric fields, giving rise to very low excess noise factors, of around F~3.3 at a multiplication factor of M~15.5 in the structure with w=0.026 μm. This is the lowest reported excess noise at this value of multiplication for devices grown on GaAs substrates. Recursion equation modeling, using both a hard threshold dead space model and one which incorporates the detailed history of the ionizing carriers, is used to model the nonlocal nature of impact ionization giving rise to the reduction in excess noise with decreasing w. Although the hard threshold dead space model could reproduce qualitatively the experimental results, better agreement was obtained from the history-dependent model     

All-GaAs/AlGaAs readout circuit for quantum-well infrared detectorfocal plane array

We report the fabrication and testing of an all-GaAs/AlGaAs hybrid readout circuit operating at 77 K designated for use with an GaAs/AlGaAs background-limited quantum-well infrared photodetector focal plane array (QWIP FPA). The circuit is based on a direct injection scheme, using specially designed cryogenic GaAs/AlGaAs MODFET's and a novel n⁺ -GaAs/AlGaAs/n⁺-GaAs semiconductor capacitor, which is able to store more than 15 000 electrons/μm² in a voltage range of ±0.7 V. The semiconductor capacitor shows little voltage dependence, small frequency dispersion, and no hysteresis. We have eliminated the problem of low-temperature degradation of the MODFET I-V characteristics and achieved very low gate leakage current of about 100 fA in the subthreshold regime. The MODFET electrical properties including input-referred noise voltage and subthreshold transconductance were thoroughly tested. Input-referred noise voltage as low as 0.5 μV/√Hz at 10 Hz was measured for a 2×30 μm² gate MODFET. We discuss further possibilities for monolithic integration of the developed devices