Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
1997-06-19
2001-05-08
Guay, John (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S627000
Reexamination Certificate
active
06229153
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains generally to the field of semiconductor devices and more particularly to resonant tunneling diodes.
BACKGROUND OF THE INVENTION
Resonant tunneling diodes comprise semiconductor structures having two large band-gap barrier layers with a single low band-gap quantum well between them. Collector
30
and emitter
31
contact regions are provided in the semiconductor structure to provide collection and supply of electrons as illustrated in the simplified band diagram of FIG.
1
. The thicknesses of barrier layers
34
and
35
and the thickness of the quantum well
36
between them, and the composition of these structures, are chosen so that quantum effects create a single resonant energy level
37
slightly above the emitter conduction band edge
38
. As the emitter
31
is negatively biased, the two bands will come into alignment at a peak voltage V
p
, as illustrated in
FIG. 2
, and electrons will tunnel through to the collector region
30
where they are collected. As the negative bias is increased still further, the emitter conduction band
38
rises above the resonant energy level
37
, as illustrated in
FIG. 3
, drastically reducing the tunneling current. The result is a negative resistance region that creates the utility of the resonant tunneling diode (RTD). As the emitter bias is increased still further, current will rise again as electrons are emitted over the barrier.
FIG. 4
shows a typical current-voltage relationship curve
40
for a typical RTD.
The high speed voltage transition occurs when the RTD is switched from the stable point “a” in
FIG. 4
to the stable point “b”. The voltage swing is maximized by making the voltage V
p
low and the voltage V
v
high. Switching speed is maximized by making the peak current I
p
as large as possible for a given conduction area. The valley current at the voltage V
v
is of great significance for high-speed applications, and should be as low as possible to maximize the current available to charge the load capacitance thus reducing the switching time.
It is desirable that RTDs be highly reliable and stable over time and with temperature changes, and have typical performance characteristics that include voltage swings of one to two volts, peak current densities of 100 to 200 kA/cm
2
, peak currents of 10 to 20 mA, peak voltages of 1 volt, peak to valley current ratios of at least 3, and a rise time of less than 2 picoseconds. Such characteristics have been achieved previously in devices made of pseudomorphic AlAs/InAs/AlAs quantum wells fed by lattice-matched InGaAs contact layers, and grown on InP by molecular beam epitaxy. However, the InP material system is not well suited for practical applications, and the technology is immature. GaAs would be ideal, but GaAs/AlAs RTDs cannot reach the performances of InP-based devices.
SUMMARY OF THE INVENTION
The resonant tunneling diode (RTD) of the present invention combines all of the desirable characteristics for such a diode in a single device which can be produced in a gallium arsenide material system using the processing techniques compatible with large scale production, particularly metal organic chemical vapor deposition (MOCVD). The device is capable of peak current densities in excess of 300 kA/cm
2
at relatively low peak voltages in the range of 1 volt. Switching times in the range of 1 picosecond can be obtained.
The multilayer RTD structure preferably is formed of barrier layers of AlGaAs with a quantum well layer formed of low band-gap material between them. The material of the well is selected to adjust the second energy level to, i.e., at or slightly above, the edge of the conduction band in GaAs. A preferred material for the quantum well layer is InGaAs. The RTD structure is grown by an MOCVD process on the surface of a nominally exact (100) GaAs substrate. To complete the device, layers of doped GaAs may similarly be formed on either side of the multilayer RTD structure. Spacer layers of GaAs may also be provided as part of the RTD structure on either side of the barrier layers to reduce the intrinsic capacitance of the structure.
It has been found that in the present invention a structure grown by the MOCVD process on the exact (100) GaAs substrate will produce smooth interfaces between the various layers, including the strained layer quantum well structure, to allow the achievement of high current density and other desirable characteristics at conventional operating temperatures (e.g., 300 K). The resulting structure provides resonant tunneling through the second energy level in a strained-layer quantum-well. The growth of strained-layer InGaAs quantum well structures using exact on-orientation substrates produces distinct layers with relatively abrupt transitions at interfaces, significantly improving the smoothness of the interfaces and consequent device performance over devices which are grown off-orientation. Specifically, rough interfaces cause carrier scattering which significantly increases the valley current and thus makes the device impractical. By smoothing the interfaces, high peak-to-valley ratios can thus be obtained.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4929984 (1990-05-01), Muto et al.
patent: 4959696 (1990-09-01), Frensley et al.
patent: 5031005 (1991-07-01), Futatsugi et al.
patent: 5569954 (1996-10-01), Hata et al.
patent: WO 89/02654 (1989-03-01), None
L.J. Mawst, et al., “High Continuous Wave Output Power InGaAs/InGaAs/InGaP Diode Laser: Effect of Substrate Misorientation,” Appl. Phys. Lett. vol. 67, No. 20. Nov. 13, 1995, pp. 2901-2903.
Francis G. Celii, et al., Optical Diagnostic Monitoring of Resonant-Tunneling Diode Growth, IEEE J. Selected Topics in Quantum Electronics, vol. 1, No. 4, pp. 1064-1072, Dec. 1995.
A. Bhattacharya, et al., Interface structures of InGaAs/InGaAsP/InGaP quantum well laser diodes grown by metalorganic chemical vapor deposition of GaAs substrates, Appl. Phys. Lett. 68 (16), pp. 2240-2242, Apr. 15, 1996.
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J.W. Lee, et al., “Molecular-Beam Epitaxial Growth of AlGaAs/(In, Ga)As Resonant Tunneling Structures,” J. Vac. Sci. Technol. B, vol. 5, No. 3, May/Jun. 1987, pp. 771-774.
R.M. Kapre, et al., “High Strained (InAs)M/(GaAs)NMultiple Quantum Well Based Resonant Tunneling Diodes On GaAs (100) Substrates and Their Applications in Optical Switching,” Met. Res. Soc. Symp. Proc., vol. 228, 1992, pp. 219-224.
E. Lheurette, et al., “In0.1Ga0.9As/GaAs/AlAs Pseudomorphic Resonant Tunneling Diodes Integrated with Air-Bridge,” Electron. Lett., vol. 28, pp. 937-938, 1992.
Botez Dan
Mawst Luke J.
Mirabedini Ali R.
Foley & Lardner
Guay John
Wisconsin Alumni Research Corporation
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