Fabrication of high-performance Al/sub x/Ga/sub 1-x/As/In/sub y/Ga/sub 1-y/As/GaAs resonant tunneling diodes using a microwave-compatible technology

Abstract

A new microwave-compatible process for fabricating planar integrated resonant tunneling diodes (RTD's) is described. Successful fabrications of high-performance RTD's using AI,Ga, -,As/ In yGa, -,As/GaAs strained layers have been obtained. Peak-to-valley current ratios (PVR's) of 4.8:l with simultaneous peak current densities of 4 x lo4 A/cm* have been achieved at room temperature for diodes of area 9 pm2. Accurate measurements of reflection gain versus frequency between 1.5 and 26.5 GHz in the negative differential region indicate that the present technology is promising for millimeter-wave integrated circuits including self-oscillating mixers, frequency multipliers, and detectors.NTEGRATION of a resonant tunneling diode (RTD) in a I planar technology is attractive for several reasons. This is primarily because a planar structure is suitable for the realization of integrated microwave and millimeter-wave functions such as mixers, harmonic multipliers, and detectors. This is also because stable and high-frequency operation can be expected owing to the reduction of parasitic reactances. In addition, if the devices are fabricated with the necessary coplanar lines for microwave wafer probing, the overall reliability and accuracy of microwave measurements will be greatly improved because spurious selfoscillations will be eliminated in a large fraction of the negative differential resistance (NDR) bias range. Recently, there has been a proposal for a microwave-compatible process employing topside contacts and proton implantation resulting in isolated devices and transmission-line interconnections [ 11. At room temperature, the devices using AlAs-GaAs double-barrier heteroepitaxies exhibit a very high peak current density of about lo5 A/cm2 with peak-to-valley current ratios (PVR's) from 2 to 2.5.In this paper, we propose a new fabrication technology that can be used for the embedding of a RTD in a low-loss transmission-line environment. For the double-barrier resonant tunneling structure, Al,Ga, -,As/In,Ga, -,As/GaAs strained layers are grown on a semi-insulating (SI) substrate that serves as the IEEE Log Number 9142892. dielectric of transmission lines. A two-step mesa technology is used for the implementation of the transmission lines directly on the SI substrate. This avoids the proton isolation proposed in [l] that provides a nonconducting dielectric for transmission lines. In other respects passive elements such as tuning inductors could be incorporated onto the chip. We demonstrate that planar monolithic integrated RTD's with high current capability can be fabricated using this microwave-compatible technology and we report unique stable frequency variations of impedance of diodes biased in the negative resistance.The epitaxial material was grown by molecular beam epitaxy in a Varian GEN-I1 system. We start from a semi-insulating [loo], 2-in, substrate. The first layer grown was a highly doped layer (No = 2 x lo'* ~m -~) of GaAs of 1 pm followed by 50-nm-thick GaAs with a doping concentration of 2 x lo', ~m -~. S...

Resonant tunneling diodes as sources for millimeter and submillimeter wavelengths

“…As last stages some of the samples were thinned to a thickness of about 120 um and polyimide was used to surround the diodes in order to aid whisker contact. For the epilayers on S-I substrate, the diodes were fabricated in a microwave-compatible two-step mesa technology [9]. In that case, the devices were connected to low-loss transmission lines in such a way that they can be characterized at the wafer level.…”

Quantum well devices for millimetre wave applications

“…In order to improve the performance of quantum devices, several proposals have also been made to integrate the device in a planar technology [ 71 [8 ]. Monolithic integration of double barrier heterostructure is attractive for several reasons.…”

“…The process reveals anisotropic and the conditions used here with a nearly perfect vertical etch of mesas. 'I'pically, anode diameters in the range of 2 to 5 im were implemented by means of this method into lOOxiOO un' matrix of dots.In order to improve the performance of quantum devices, several proposals have also been made to integrate the device in a planar technology [ 71 [8 ]. Monolithic integration of double barrier heterostructure is attractive for several reasons.…”