SAM APD Research Articles

Dependence of electrical field and photoresponse on multiplication region thickness for GaN APDs

A visible-blind ultraviolet GaN back-illuminated avalanche photodiode with separate absorption and multiplication regions (SAM APDs) are simulated based on drift-diffusion equation. The current–voltage characteristics of the device have been numerically obtained. The result is in good agreement with the experimental data. It was found that the thickness of the multiplication layer is important to improve the electrical field profiles and spectral response characteristics. A peak responsivity of 106.5 mA/W is achieved at 364 nm corresponding to the cutoff wavelength of GaN.

Effect of Interface Polarization Charge on GaN/SiC Separate Absorption and Multiplication Avalanche Photodiodes

A III-Nitride/ SiC separate absorption and multiplication avalanche photodiode (SAM-APD) offers a novel approach for fabricating high gain photodetectors with tunable absorption over a wide spectrum from the visible to deep ultraviolet. However, unlike conventional heterojunction SAM APDs, the formation of polarization-induced charge at the hetero-interface arising from spontaneous and piezoelectric polarization can dramatically affect the performance of this detector. In this paper we report on the role of this interface charge on the performance of GaN/SiC SAM APDs.

III-NITRIDE/SiC SEPARATE ABSORPTION AND MULTIPLICATION AVALANCHE PHOTODIODES: THE IMPORTANCE OF CONTROLLING POLARIZATION-INDUCED INTERFACE CHARGE

A III-Nitride/ SiC separate absorption and multiplication avalanche photodiode (SAM-APD) offers a novel approach for fabricating high gain photodetectors with tunable absorption over a wide spectrum from the visible to deep ulltraviolet. However, unlike conventional heterojunction SAM APDs, the formation of polarization-induced charge at the hetero-interface arising from spontaneous and piezoelectric polarization can dramatically affect the performance of this detector. In this paper we report on the role of this interface charge on the performance of GaN / SiC SAM APDs. Simulations of the electric field profile within this device structure while biased near avalanche breakdown indicate that the density of positive interface charge may be sufficient to confine the electric field within the SiC multiplication region with negligible punch-through into the GaN absorption region, a distribution that is likely undesirable for efficient collection of photo-generated holes due to the presence of defects at the hetero-interface. Simulations further show that the incorporation of a p -type doped interface charge control layer at the hetero-interface can modify the total density of charge at the interface and allow for the tailoring of the electric field profile within this device. Experimental results are provided that correlate well with the simulation results.

Avalanche Noise Characteristics in Submicron InP Diodes

We report excess noise factors measured on a series of InP diodes with varying avalanche region thickness, covering a wide electric field range from 180 to 850 kV/cm. The increased significance of dead space in diodes with thin avalanche region thickness decreases the excess noise. An excess noise factor of F = 3.5 at multiplication factor M = 10 was measured, the lowest value reported so far for InP. The electric field dependence of impact ionization coefficients and threshold energies in InP have been determined using a non-local model to take into account the dead space effects. This work suggests that further optimization of InP separate absorption multiplication avalanche photodiodes (SAM APDs) could result in a noise performance comparable to InAlAs SAM APDs.

RECENT DEVELOPMENT OF SB-BASED PHOTOTRANSISTORS IN THE 0.9- TO 2.2-μM WAVELENGTH RANGE FOR APPLICATIONS TO LASER REMOTE SENSING

We have investigated commercially available photodiodes and also recent developed Sb -based phototransistors in order to compare their performances for applications to laser remote sensing. A custom-designed phototransistor in the 0.9- to 2.2-μm wavelength range has been developed at AstroPower and characterized at NASA Langley's Detector Characterization Laboratory. The phototransistor's performance greatly exceeds the previously reported results at this wavelength range in the literature. The detector testing included spectral response, dark current and noise measurements. Spectral response measurements were carried out to determine the responsivity at 2-μm wavelength at different bias voltages with fixed temperature; and different temperatures with fixed bias voltage. Current versus voltage characteristics were also recorded at different temperatures. Results show high responsivity of 2650 AIW corresponding to an internal gain of three orders of magnitude, and high detectivity (D*) of 3.9×1011 cm.Hz 1/2/ W that is equivalent to a noise-equivalent-power of 4.6×10-14 W/Hz 1/2 (-4.0 V @ -20°C) with a light collecting area diameter of 200-μm. It appears that this recently developed 2-μm phototransistor's performances such as responsivity, detectivity, and gain are improved significantly as compared to the previously published APD and SAM APD using similar materials. These detectors are considered as phototransistors based-on their structures and performance characteristics and may have great potential for high sensitivity differential absorption lidar (DIAL) measurements of carbon dioxide and water vapor at 2.05-μm and 1.9-μm, respectively.

InGaAs/InP photodiodes grown by metalorganic chemical vapor deposition

InGaAs/InP heterostructure p-i-n photodiodes and two types of InGaAs/InP avalanche photodetectors have been fabricated from structures grown by atmospheric-pressure metalorganic chemical vapor deposition. The p-i-n photodetectors are diffused p-n junction devices of 75 μm diameter and have low dark currents ( ∼ 10 nA at - 10V), good quantum efficiencies ( ∼ 50% without anti-reflectance coatings), and response times less than 40 ps. The avalanche photodiodes with separate absorption and multiplication regions (SAM APD's) have shown the two-component pulse response that is typical of this type of structure with the fast component being 100 ps and the slow component being 6ns. This slow component has been eliminated by incorporating an intermediate-band-gap transition region between the absorption and multiplication regions. The APD's exhibit low dark currents ( ∼ 32 nA at 90% of breakdown) and high-speed response ( ∼ 100 ps FWHM).

Avalanche photodiodes with separate absorption and multiplication regions grown by metalorganic vapor deposition

InP/InGaAs avalanche photodiodes with separate absorption and multiplication regions (SAM APD's) have been fabricated from wafers grown by atmospheric-pressure metalorganic chemical vapor deposition. These APD's exhibit low dark current and good quantum efficiency. The pulse response exhibits the two-component response typical of the SAM-APD structure. The slow component is 6 ns and the fast component is 100 ps.

Impact ionization rates for electrons and holes in Al0.48In0.52As

The first measurement of the impact ionization rates for electrons and holes in Al0.48In0.52As is reported. Photomultiplication measurements in pin avalanche photodiodes give α/β≊2.5–3.0 in the electric field range 3.3×105 V/cm≤F≤4.3×105 V/cm. This material can therefore be used to implement a potentially high-performance, long-wavelength avalanche photodiode, with separate absorption and multiplication regions and a high-low electric field profile (HI-LO SAM APD).

New low dark current, high speed Al0.48In0.52As/ Ga0.47In0.53As avalanche photodiode by molecular beam epitaxy for long wavelength fiber optic communication systems

We report a new Al0.48In0.52As/Ga0.47In0.53As avalanche photodiode with separate absorption and multiplication regions (SAM APD) and an undoped spacer layer in the gain region. These devices grown by molecular beam epitaxy, have very low dark currents (4 nA at the onset of gain) which compare favorably with state-of-the-art InP/Ga0.47In0.53As SAM APD’s. Avalanche gains ≊60 and a high speed of response with a gain-bandwidth product ≊10 GHz are demonstrated. Receiver sensitivity measurements at 420 Mb/s and λ=1.3 μm with a Si bipolar transistor preamplifier yielded −36.0 dBm at a 10−9 bit error rate.

Low-dark-current low-voltage 1.3–1.6 μm avalanche photodiode with high-low electric field profile and separate absorption and multiplication regions by molecular beam epitaxy

The operation of the recently disclosed heterojunction avalanche photodiode with high-low electric field profile and separate absorption and multiplication regions (HI-LO SAM APD) is demonstrated. This new structure which features a doping spike in the wide gap layer offers several advantages over conventional SAM APDs (lower dark current and excess noise factor, greater gain stability). Low dark currents (≃1 nA), low voltage operation (−26 V) and gains as high as 50 at 1.60 μm are demonstrated in an Al0.48In0.52As/Ga0 47In0 53As prototype grown by molecular beam epitaxy.