GaAlAs/GaAs heterojunction microwave bipolar transistor

A GaAlAs/GaAs heterojunction bipolar transistor has been developed and tested. A double base structure was adopted to facilitate critical selective etching problems. An emitter-collector breakdown voltage VCEO as high as 80 V was achieved. Maximum frequency of oscillationfmax of 850 MHz and a cutoff frequency fT of 1.6 GHz were realised. The current-gain/temperature curve shows that the transistor can be operated at temperatures up to 350°C.     

Double heterojunction NpN GaAlAs/GaAs bipolar transistor

Double heterojunction NpN Ga0.7Al0.3As/GaAsAs/Ga0.7Al0.3-As bipolar transistors have been developed and tested. Besides a wide-gap emitter a wide-gap collector was added to form the NpN double heterojunction structure, which can be operated as a bipolar transistor in bidirection. I/V measurements show that the turn-on voltage of about 0.2 V, which is the normal case in Npn wide-gap emitter GaAsAs/Ga0.7Al0.3As transistors (common emitter), is eliminated. As compared with the Npn GaAs transistor the storage time ts of the NpN GaAs transistor is reduced by a factor of about 2.     

Carrier-Transport Processes in n+-GaAs/n0-GaAs/n+-GaAs Isotype Heterostructures with a Thin Wide-Gap AlGaAs Barrier

Semiconductors - Experimental studies of n+-GaAs/n0-GaAs/n+-GaAs isotype heterostructures with a 100-nm-thick wide-gap N0-AlGaAs barrier situated in the n0-GaAs region are carried out. It is shown...     

Electrical behavior of an NPN GaAlAs/GaAs heterojunction transistor

This paper deals with a theoretical and experimental study of GaAlAs/GaAs heterojunction transistors fabricated by liquid phase epitaxy.Starting from the general transport equations in a structure of variable composition, the expressions for the injection efficiency and for the transfer characteristic (I_C, V_BE) are first established. Using reasonable simplifying assumptions, allowed by the physical characteristics of the base and emitter regions, the major role played by the zone including the conduction band spike is clearly shown. In particular, it appears that the presence of such a spike entails a substantial decrease of the injection efficiency and also modifies, over a wide bias range, the (I_C, V_BE) characteristic which then follows a non ideal law.The experimental behaviour of devices fabricated by liquid phase epitaxy are described. The measurements were carried out at temperatures ranging from 77 to 316°K. The results obtained are compared with those predicted by the theoretical model.     

A high voltage-gain GaAs vertical field-effect transistor with anInGaAs/GaAs planar-doped barrier launcher

A high voltage-gain GaAs vertical field-effect transistor (VFET) with an InGaAs-GaAs pseudomorphic planar-doped barrier (PDB) launcher is described. The pseudomorphic structure, which includes a small amount of indium in the launcher, was grown by molecular beam epitaxy (MBE). Fabricated transistors, with good pinch-off characteristics (gate threshold voltage of -1.6 V), have exhibited DC open-drain voltage gains of up to 50 at 77 K. This high voltage gain results from the combination of high transconductances and low output conductances. The former are attributed to velocity enhancement by hot-electron injection, and the latter are attributed to the suppression of electron spillover by energy band discontinuity at the heterointerface between the launcher and the channel     

Model of the diode-connected GaAs Schottky-gate field-effect transistor

A model of the diode-connected GaAs Schottky-gate field-effect transistor (SFET) has been proposed. The SFETs with uniform and δ-doped channels are considered. The model accounts for the distributive character of the channel’s resistive regions under the gate and the passive contact regions between the gate and the ohmic contact. Based on the results obtained, the equivalent circuit of the diode-connected SFET, which accounts for the current displacement effect, and the method to measure its parameters have been suggested. The model may be used for heterostructure FETs with high electron mobility in the channel (HEMT).     

Monte Carlo simulation of GaAs submicron n+-n-n+ diode with GaAlAs heterojunction cathode

A Monte Carlo simulation program has been developed to simulate the motion of electrons in a submicron GaAs diode with a Ga1?xAlxAs heterojunction cathode. It is shown that the hot electron injection through the heterojunction cathode is effective to increase the mean electron velocity of carriers.     

Multiple-energy proton bombardment in n+-GaAs

The effects of single-energy and multiple-energy proton bombardment on the electrical characteristics of n⁺-GaAs (n ≥ 10¹⁸ cm^?3) have been studied. It was found that a multiple-energy bombardment is superior to a single-energy bombardment in creating high-resistivity layers in n⁺-GaAs. For 4 × 10¹⁸ cm^?3 GaAs, the entire 4-μm-thick bombarded layer could not be effectively compensated by a single-energy 400-keV bombardment. A multiple-energy bombardment, however, effectively compensated the bombarded layer throughout its depth. With no annealing, there is a optimum multiple-bombardment dose which maximizes the average resistivity. With annealing, higher doses are necessary and for a dose higher than the optimum without annealing, the resistivity at first increases and then goes through a maximum with increasing anneal temperature. There is again an optimum dose for any specific anneal temperature and for the range of doses studied, the resistivity reaches a maximum at a higher anneal temperature for increasing total dose. For n⁺-GaAs with an initial concentration of 10¹⁸ cm^?3, layers with an average resistivity of $\text{≥ 10}{}^8\text{Ω-}\text{cm}$ have been achieved using a multiple-energy bombardment and an anneal temperature as high as 500°C. Measurement of the ac resistivity as a function of frequency indicates that conduction in the bombarded layer may be occurring via a hopping mechanism.     

Planar monolithic integration of a GaAs photoconductor and a GaAs field-effect transistor

A planar monolithic integrated photoreceiver suitable for 0.8 ?m-wavelength optical communication systems has been realised. It consists of a GaAs photoconductor associated with a GaAs FET. The steady state and dynamic gains and the noise properties of the photoconductor and of the integrated circuit have been investigated.     

Monolithic integration of GaAs photoconductors with a field-effect transistor

A one-stage monolithic integration of a tandem pair of GaAs photoconductors (PCs) with a field-effect transistor (FET) is reported. The PC-FET exhibits a bandwidth in excess of 1 GHz and a gain of 6 dB at midband. A very low noise figure of ~3 dB in the FET is also achieved.     

GaAs/GaAlAs active-passive-interference laser

A GaAs/GaAlAs interference laser with an active and a passive section is reported. A very clean single longitudinal mode is obtained and maintained without mode hopping over about 10°C, which results from the combined effect of interference and real index waveguiding in the lateral direction.     

Output-resistance properties of the GaAs Schottky-gate field-effect transistor in saturation

Some new experimentally observed properties of the output resistance of GaAs Schottky-gate f.e.t.s in saturation are described. A phenomenological model is proposed in which the structure is divided into two sections: a source section, where the approximation is assumed to be gradual, and a drain section, where the drain current is included in the `equivalent doping?. At high drain currents, the experimental results are found to correspond well with the theory.     

Emitter—Base bandgap grading effects on GaAlAs/GaAs heterojunction bipolar transistor characteristics

Emitter-base bandgap grading effects on GaAlAs/GaAs heterojunction bipolar transistor characteristics are theoretically investigated using an accurate one-dimensional numerical model including aluminum mole-fraction-dependent velocity versus field characteristics and donor energy level. The bandgap grading is shown to influence not only the electron injection but also the carrier recombination and the hole injection, resulting in a significant common-emitter current gain dependence on the graded layer thickness. The cutoff frequency dependence on the graded layer thickness is also described. Detailed discussion is given for the underlying physical mechanism that determines the device performance.     

Luminescence of stepped quantum wells in GaAs/GaAlAs and InGaAs/GaAs/GaAlAs structures

Luminescence spectra of doped and undoped GaAs/GaAlAs and InGaAs/GaAs/GaAlAs structures containing several tens of stepped quantum wells (QW) are investigated. The emission bands related to free and bound excitons and impurity states are observed in QW spectra. The luminescence excitation spectra indicate that the relaxation of free excitons to the e1hh1 state proceeds via the exciton mechanism, whereas an independent relaxation of electrons and holes is specific to bound excitons and impurity states. The energy levels for electrons and holes in stepped QWs, calculated in terms of Kane’s model, are compared with the data obtained from the luminescence excitation spectra. The analysis of the relative intensities of emission bands related to e1hh1 excitons and exciton states of higher energy shows that, as the optical excitation intensity increases, the e1hh1 transition is more readily saturated at higher temperature, because the lifetime of excitons increases. Under stronger excitation, the emission band of electron-hole plasma arises and increases in intensity superlinearly. At an excitation level of ～10⁵ W/cm², excitons are screened and the plasma emission band dominates in the QW emission. Nonequilibrium luminescence spectra obtained in a picosecond excitation and recording mode show that the e1hh1 and e2hh2 radiative transitions are 100% polarized in the plane of QWs.     

GaAs/GaAlAs curved rib waveguides

Curved dielectric optical waveguides suffer from radiation loss due to bending. To minimize the bending loss and reduce the radius of curvature, it is necessary to fabricate guides which provide strong optical confinement. This paper gives a brief review of curved waveguide analysis and presents some experimentally measured loss values for GaAs/GaAlAs curved rib waveguides. The rib waveguides, fabricated using ion beam milling, have a large rib height and are tightly guided structures. When corrected for reflection losses and input coupling efficiency, a minimum loss of approximately 3 dB has been achieved for a multimode 90° curved guide with a radius of curvature of 300 μm, and 8.5 dB for a single-mode curved guide with a radius of curvature of 400 μm. It is believed that most of this residual loss is not radiation loss due to bending, but rather scattering loss due to rib wall imperfections.     

Ambipolar field-effect transistor

The results of measurements performed on an amorphous-silicon thin-film transistor structure are presented and interpreted. The device characteristics show a continuous alternation between n-channel and p-channel operation, an “ambipolar” effect that is made possible by the provision of ohmic source and drain contacts.     

Vacuum-insulated-gate field-effect transistor

A vacuum-insulated-gate field-effect transistor (VIGFET) is fabricated using a modified polysilicon-gate MOS process. The vacuum insulation is formed by first selectively etching the initial SiO/sub 2/ layer under the polysilicon gate in HF and then depositing LPCVD SiO/sub 2/ (LTO) to seal the evacuated cavity under the gate. Initial measurements of n-channel FET drain characteristics result in an effective value for the channel-electron mobility*gate capacitance product of k'= mu /sub n/C'=21 mu A V/sup -2/, comparable to that of conventional MOSFETs.<>     

Inversion-channel Si/SiGe heterojunction field-effect transistor

The p-channel operation of a selfaligned heterojunction field-effect transistor (HFET) based on an Si/Si/sub 0.75/Ge/sub 0.25/ heterostructure is demonstrated. Extrinsic transconductance g/sub m/ greater than 8 mS/mm for a device with 1 mu m gate length was measured at 300 K. The high frequency 3 dB point has been measured to be 1.8 GHz.<>     

Band-bending effect of low temperature GaAs on a pseudomorphic modulation-doped field-effect transistor

Low temperature photoluminescence (PL) measurements on pseudomorphic modulation-doped transistors with a low-temperature (LT) GaAs layer in the GaAs buffer layer clearly show a decrease in the quantum well PL transition energies compared to a structure with no LT GaAs. Self-consistent calculations of the electron and hole bandstructure suggest that the observed increase in the redshift in PL energies with increasing quantum well-LT GaAs spacing can be attributed to band bending induced by the Fermi level pinning at the undoped GaAs/LT GaAs interface and a novel carrier compensation effect of LT GaAs.     

Impedance and noise in the channel of a GaAs Schottky-gate field-effect transistor

The behaviour of the impedance and noise of the channel of a GaAs Schottky-gate field effect transistor is experimentally analyzed in the temperature range 77–300K and in the frequency range of 150 to 900 MHz. The channel of the transistor (source and gate being short circuited) shows a thermal noise level in good agreement with van der Ziel's theory. At 77K, the observed excess of the noise temperature is attributed to an effect of hot carriers.