A technique for the liquid‐phase epitaxial growth of thin GaAs layers has been developed. This technique uses supercooled solutions free from GaAs precipitates. With the amount of the initial supercooling in the range of 1–10 °C, very smooth surfaces with a roughness smaller than 0.01 μm are obtained for layers thinner than 1μm. The layer thickness data agree well with the diffusion theory equation by assuming that the diffusion coefficient of As in Ga is 4×10−5 cm2/sec at 800 °C. The thickness uniformity within a wafer is better than ±5%, and the thickness reproducibility among different runs is within ±7%. The carrier concentration is also well controlled.

Liquid-phase epitaxial growth of thin GaAs layers from supercooled solutions

A double epitaxial gallium arsenide tuning diode has been developed for TV varactor tuners. The capacitance variation ratio is 6.0 and is large enough to cover the UHF TV broadcasting band. Diode series resistance is 0.18 Ω ( Q = 200 ) at 470 MHz, and at a capacitance of 9 pF. This resistance is 4.4 times smaller than Si diodes in its mean value. Contribution of each resistance component to the total diode resistance was studied. The result shows that package loss is 0.11 Ω, RF skin-effect resistance is 0.05 Ω, and the undepleted epitaxial layer resistance is 0.048 Ω. Therefore, a diode with a 0.075-Ω ( Q = 480 ) series resistance at 470 MHz could be developed, if package loss and RF skin-effect resistance are improved.

High-Q GaAs varactor diodes

In this review some of the factors which are important in ion implantation doping of III–V compound semiconductors will be discussed Emphasis will be placed on the results so far obtained in GaAs A discussion of the results in other III–V materials will be included as well as some comments on the application of ion implantation to the fabrication of devices in semiconducting III–V compounds

Ion Implantation In III–V Compounds

Gallium arsenide varactor diodes with low series resistance (∼0.25 Ω) for u.h.f. t.v. tuners are developed. Uniformity and reproducibility of diode capacitance is improved markedly by using improved ion implantation and l.p.e. techniques. The standard deviation of diode capacitance distribution is 0.74% at V = 3.0 V within a wafer. A good r.f. tracking characteristic can be obtained in varactor tuners.

Ion implanted GaAs varactor diodes: capacitance uniformity

Recently, varactor tuners have become very popular in TV tuner, but the noise figure and selectivity of present day's varactor tuners are inferior to that of mechanical tuners. Series resistance, Rs, of Si tuning diodes manufactured is around 0.8?in mean value at 470 MHz and at diode capacitance of 9 pF. The value of 0.8?is so high that low resistance diodes, Rs < 0.8?, for instance, have been selected specifically for UHF tuners. Recently, low resistance diodes with Rs = 0.68?have been fabricated by ion implantation technique. 1) Even if these diodes are employed, the Q value of tuning circuit is still much lower than that of mechanical tuner in UHF region. Such high resistance diodes lead to a higher noise figure and lower gain in tuner performance.

GaAs Varactor Tuners for UHF TV

Gallium-arsenide varactor diodes have been developed by using ion implantation techniques. Diode series resistance is around 0.25 Ω and uniform among diodes. The standard deviation of resistance distribution is 11.6%. Capacitance variation ratio, C3/C25, is about 5.7.

GaAs varactor diodes for u.h.f. TV tuners fabricated by ion implantation

The design and fabrication of a GaAs varactor diode for u.h.f. t.v. tuners were carried out using a GaAs double epitaxial layer. The capacitance ratio of diode. C3/C25, is 6.0 and the series resistance at 470 MHz is 0.24 Ω. These characteristics are much better than those of an Si diode and well satisfy the requirements for t.v. tuners.

GaAs varactor diode for u.h.f. t.v. tuners

There is an urgent demand for low noise varactor tuners for use in TV receivers to meet the requirements of FCC rules. The RF amplifier has been frequently eliminated in mechanical tuners now in use, resulting in good cross-modulation characteristics and low cost. However, the elimination of the RF amplifier has not been attained in varactor tuners, because of high series resistance of varactor diodes. The series resistance of Si diodes at 470 MHz is around 0.7?,and is much higher than that of mechanical capacitor, 0.15?. To reduce the noise figure of varactor tuners, tuning diodes with low resistance, i. e. below 0.2?must be developed. However, few reports have been published on low series resistance diodes for UHF use.

Ikuo Niikura

Papers

GaAs varactor diodes for u.h.f. TV tuners fabricated by ion implantation

Ion implanted GaAs varactor diodes: capacitance uniformity

GaAs varactor diode for u.h.f. t.v. tuners

GaAs Varactor Tuners for UHF TV

Varactor Tuners Eliminated an RF Amplifier