It is shown that optimization of the electric field profile in the absorption region of separate absorption, charge, and multiplication InGaAs-InAlAs avalanche photodiodes is critical to achieve low excess noise and high gain bandwidth product.

We report single photon counting in p-n junction 4H-SiC avalanche photodetectors. At 325 nm, the unity-gain external quantum efficiency was 10% and the single photon detection efficiency was 2.9%. This result represents /spl sim/30% of the maximum attainable detection efficiency.

Electron-assisted chemical etching of oxidized chromium, CrOx, has been studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). Two model substrates were used—10nm CrOx deposited on Si(100) that was covered with either native oxide or a 20nm Au/Pd alloy film. Using chlorine and/or oxygen as etching gases, the experiments were conducted in a customized high vacuum system, equipped with a high density electron source and a low pressure reaction cell. On both substrates, electron-assisted chemical etching of CiOx was detected by SEM, EDS and AFM. Making the method questionable for etching applications, there is substantial substrate damage associated with the etching. The SEM images indicate strongly inhomogeneous material removal, apparently initiated and propagated from specific but unidentified sites. In the experiments involving the Au/Pd film, there was phase separation of Au and Pd, and dewetting to form metallic islands. AFM data show that the etched holes were as deep as 200nm, confirming relatively rapid etching of the Si substrate after the top layer of Cr oxide was removed.

In a 3keV electron system, we have studied both electron beam induced CrOxCly deposition using precursor CrO2Cl2 and electron beam induced etching of as-deposited CrOxCly film using Cl2. The CrO2Cl2 pressure, 6.5×10−5Torr, was experimentally observed to be a threshold for CrOxCly deposition. The Cr film is a composite of Cr, O and Cl with a ratio of Cr:O:Cl=1:2.2:1.1, and under electron beam irradiation, O increases while Cl decreases. As-deposited CrOxCly films can be etched in situ by chlorine at a pressure of 6×10−4Torr with an electron flux of 10mAcm−2, demonstrating that Cl2 pressure is the key in initiating the etching reaction.

This study demonstrates 1.52 μm Geiger mode operation of an In0.53Ga0.47As/In0.52Al0.48As APD. A study of the origin of dark count rate in this detector is also presented.

Large-area (500-/spl mu/m diameter) mesa-structure In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiodes (APDs) are reported. The dark current density was /spl sim/2.5/spl times/10/sup -2/ nA//spl mu/m/sup 2/ at 90% of breakdown; low surface leakage current density (/spl sim/4.2 pA//spl mu/m) was achieved with wet chemical etching and SiO/sub 2/ passivation. An 18 /spl times/ 18 APD array with uniform distributions of breakdown voltage, dark current, and multiplication gain has also been demonstrated. The APDs in the array achieved 3-dB bandwidth of /spl sim/8 GHz at low gain and a gain-bandwidth product of /spl sim/120 GHz.

We report an avalanche photodiode with an undepleted p-type InGaAs absorption region and a thin InAlAs multiplication layer. The motivation for utilizing an undepleted absorption layer, which is similar to that in the unitraveling carrier photodiode, is to reduce the dark current. A dark current below 1 nA at a gain of 10 and a gain–bandwidth product of 160 GHz are demonstrated.

We report low noise multiplication region structures designed for avalanche photodiodes grown on InP substrates. By either implementing a single heterostructure or using a pseudograded structure in the multiplication region, better control of spatial distribution of impact-ionization for both injected and feedback carriers can be achieved; localization of the carrier impact ionization process has resulted in very low excess noise.

We report the direct growth of impact-ionization engineering (I2E) structures using InAlAs and InAlGaAs quaternary in the multiplication regions. Compared to homojunction InAlAs and InP APDs, lower excess noise and comparable dark current have been achieved.

A Monte Carlo model is developed to simulate avalanche photodiodes with AlGaAs/GaAs heterojunctions. The experimentally observed ultralow-noise behavior of a center-well avalanche photodiode is successfully reproduced in the model. It is found that the arrangement of different materials in the intrinsic region can modulate the positional dependence of impact ionization events, and hence the gain distribution. Consequently, the noise is sensitive to the structural parameters such as well thickness. Hot and energetic electrons are distinguished by their distribution in k space. This distinction is used to explain why the noise behavior is sensitive to the initial carrier excess energy from photogeneration but relatively insensitive to carrier energy gained from the electric field.

We report a 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode (APD) array. The mean breakdown voltage of the APD was 57.9 V and the standard deviation was less than 0.1 V. The mean dark current was /spl sim/2 and /spl sim/300 nA, and the standard deviation was /spl sim/0.19 and /spl sim/60 nA at unity gain (V/sub bias/ = 13.5 V) and at 90% of the breakdow...

We demonstrate an impact-ionization-engineered structure for the multiplication region of avalanche photodiodes. By enhancing the control of the impact-ionization position, the structure achieved high gain, low dark current, and very low noise.

We report high-performance back-to-back Schottky metal-semiconductor-metal photodetectors fabricated on GaN epitaxial layers grown by molecular beam epitaxy. The photodetectors exhibit very low dark current (<1 pA at 30 V) and high external quantum efficiency (>70%). Medici simulation of the depletion region width indicated an absence of photoconductive gain. The temporal response has also been characterized.