H. D. Law

III-V alloy heterostructure high speed avalanche photodiodes

Heterostructure avalanche photodiodes have been successfully fabricated in several III-V alloy systems: GaAlAs/GaAs, GaAlSb/GaSb, GaAlAsSb/GaAlSb, and InGaAsP/InP. These diodes cover optical wavelengths from 0.4 to 1.8 mu m. Early stages of development show very encouraging results. High speed response of 95 percent have been obtained. The dark currents and the excess avalanche noise will also be discussed. A direct comparison of GaAlSb, GaAlAsSb, and InGaAsP avalanche photodiodes is given.

Ion‐implanted InGaAsP avalanche photodiode

High‐quantum‐efficiency planar and mesa InGaAsP avalanche photodiodes have been fabricated by beryllium ion implantation. The implanted diodes, after suitable annealing, exhibited a very low dark current density of 4.0×10−6 A/cm2 at 10 V. The devices have 65% external quantum efficiency at 1.06 μm without an antireflection coating and a uniform avalanche gain of 12.

High sensitivity optical receivers for 1.0-1.4 µm fiber-optic systems

The performance of high-speed, high-quantum-efficiency GaAlAsSb avalanche photodetectors suitable for a 1.0-1.4 mu m high-performance fiber-optical communication system is described. The incorporation of these APDs with state-of-the-art GaAs FET electronics can lead to hybrid integrated optical receivers with 10-20 times better sensitivity at a 100-MHz bandwidth than is available with germanium APDs.

1.0–1.4‐μm high‐speed avalanche photodiodes

High‐speed high‐quantum‐efficiency avalanche photodiodes (APD’s) are required in the 1.0–1.4‐μm wavelength range in order to exploit the superior optical fibers now available at these wavelengths. The GaAlSb heterojunction APD’s reported here have external quantum efficiencies of 60% (without antireflection coatings), risetimes of 60 ps, and pulse widths (FWHM) of 120 ps with no evidence of a ’’back porch’’. Uniform high‐speed avalanche gains of 20 have been achieved.

1.33‐μm HgCdTe/CdTe photodiodes

Hg1−xCdxTe epilayers with a wavelength of ∼1.33 μm have been successfully grown by liquid phase epitaxy. Photodiodes were fabricated and measured. Analysis of the heterojunctions indicates that at room temperature the junction current at forward bias is dominated by a generation‐recombination mechanism. The generation‐recombination effective lifetime was estimated to be 2×10−7 s. A leakage current density of 9×10−6 A/cm−2 was observed at a reverse bias of 30 V, and the diode breakdown voltage was 70 V.

Ionization coefficients of Ga0.72Al0.28Sb avalanche photodetectors

The performance of an optical receiver depends heavily on the excess multiplication noise characteristics of the avalanche photodetector. The excess multiplication noise factor of an avalanche photodiode depends on the ratio of the electron and hole ionization coefficients. The ionization coefficients of 1.06‐μm photodiodes fabricated from Ga0.72Al0.28Sb have been measured. The results show a hole‐to‐electron ionization‐coefficient ratio of 2, which implies an excess gain noise factor F of 5.9 when the diode is operated at a gain of 10.

1.22‐μm HgCdTe/CdTe avalanche photodiodes

A planar HgCdTe/CdTe avalanche photodiode with peak responsivity at 1.22 μm and cutoff at 1.25 μm has been fabricated successfully by liquid phase epitaxy (LPE). Avalanche gains of higher than 15 have been obtained with 1.06‐μm Nd:yttrium aluminum garnet (YAG) laser illumination. A reverse breakdown voltage of 80 V and a leakage current density of 1×10−4 A/cm2 at 40 V were measured. The peak quantum efficiency at 1.22 μm is 72% without any antireflection coating.

State‐of‐the‐art performance of GaAlAs/GaAs avalanche photodiodes

Ga0.15Al0.85As/GaAs avalanche photodiodes have been successfully fabricated. The performance of these detectors is characterized by a rise time of less than 35 ps, an external quantum efficiency with an antireflection coating of 95% at 0.53 μm, and a microwave optical gain of 42 dB. The dark current density is in the low‐10−8‐A/cm2 range at one‐half the breakdown voltages, and rises to 1.1×10−4 A/cm2 at 42 dB optical gain.

TP-C12 GaAlAsSb/GaAlSb detectors and sources for long-wavelength fiber-optics communication

For both sizes of diodes, on-the-wafer yields of APD’s with gain have been as high as 75 percent, which indicates a high level of bulk uniformity. Subnanosecond rise and fall times, and quantum efficiencies of 70 percent at 1.27 pm have also been obtained. The leakage current density at half the breakdown voltage is extremely low, even for the larger area diodes, typical values being in the range 2-6 X A/cm2. However, at about 75 percent of the breakdown voltage, the leakage current begins to increase rapidly, and at high gains leads to excessive shot noise. The optimum operating point when used with a good low noise, broad-band (100 MHz), transimpedance amplifier typically occurs at a current gain of only 3-4, where the noise equivalent power of the APD is about 2 X lo-’’ W/Hzl/’. Noise measurements have been made and analyzed in order to determine whether the increase in leakage current is due to locally large multiplication of dark current at microplasmas, or whether it is simply due to an increase in the premultiplication dark current followed by uniform multiplication at the bulk gain. The results indicate that he increased leakage current arises from a uniformly multiplied, but increasing value of the primary (i.e., premultiplication) leakage current. The size of the primary leakage current can be derived from the noise measurements, and leads to a prediction of gain saturation in approximate agreement with the observed maximum gain. There are some indications that the leakage current is surface dominated. Guard-ring structures are being fabricated in an effort to reduce surface effects. Preliminary structures with a surface breakdown voltage 35 V higher than the interior breakdown voltage (z 5 0 V) have been fabricated, and have resulted in gains up to about 10.

Be implanted InGaAsP avalanche photodiode

High quantum efficiency planar and mesa InGaAsP avalanche photodiodes have been fabricated by beryllium ion implantation. The implanted diodes, after suitable annealing, exhibited a very low dark current density of 4.0×10-6A/cm2at 10 V. The devices have 65% external quantum efficiency at 1.06µm without an anti-reflection coating and a uniform avalanche gain of 12.