The HgCdTe electron avalanche photodiode

Extended x-ray absorption fine structure (EXAFS) investigation was carried out on two arsenic-doped HgCdTe samples. Arsenic incorporation was achieved with a non-conventional radiofrequency plasma source in a molecular beam epitaxy reactor. Both samples were taken from the same epitaxial run. One of these samples followed a 400°C activation anneal under Hg pressure. EXAFS was used here to probe the local environment around arsenic, and the experimental data were fit through first-principle calculations to extract a quantitative description of the arsenic site transfer upon annealing. Arsenic neighbors are described in terms of chemical nature, numbers and distances. Arsenic was found to be involved mostly in noncrystalline structures, either an As 2 Te 3 glass or an AsHg compact structure. The effect of annealing is to break down the chalcogenide glass, thus favoring the compact AsHg structure. EXAFS results were compared to 77 K Halleffect measurements, and a very good correlation was found. These findings were compared to the commonly admitted scenario for arsenic site incorporation and transfer upon annealing and provided a new picture and the first experimental evidence of the site transfer.

Section: Introductionmentioning

confidence: 99%

Extended X-ray Absorption Fine Structure Investigation of Arsenic in HgCdTe: the Effect of the Activation Anneal

Ballet

Polge

Biquard

et al. 2009

“…Several groups [1][2][3][4][5][6][7][8][9][10][11][12] have reported multiplication gains of M = 100 to 1000 at low values of reverse bias, around 10 V, associated with a quasideterministic multiplication which yields a conserved signal-to-noise ratio (SNR). These exceptional characteristics are due to an exclusive impact ionization of the electrons, which is why these devices have been termed electron-initiated avalanche photodiodes (e-APDs).…”

Section: Introductionmentioning

confidence: 99%

Study of the Transit-Time Limitations of the Impulse Response in Mid-Wave Infrared HgCdTe Avalanche Photodiodes

Perrais

Derelle

Mollard

et al. 2009

The impulse response in frontside-illuminated mid-wave infrared HgCdTe electron avalanche photodiodes (APDs) has been measured with localized photoexcitation at varying positions in the depletion layer. Gain measurements have shown an exponential gain, with a maximum value of M = 5000 for the diffusion current at a reverse bias of V b = 12 V. When the light was injected in the depletion layer, the gain was reduced as the injection approached the N+ edge of the junction. The impulse response was limited by the diode series resistance-capacitance product, RC, due to the large capacitance of the diode metallization. Hence, the fall time is given by the RC constant, estimated as RC = 270 ps, and the rise time is due to the charging of the diode capacitance via the transit and multiplication of carriers in the depletion layer. The latter varies between t 10-90 = 20 ps (at intermediate gains M < 500) and t 10-90 = 70 ps (at M = 3500). The corresponding RC-limited bandwidth is BW = 600 MHz, which yields a new absolute record in gainbandwidth product of GBW = 2.1 THz. The increase in rise time at high gains indicates the existence of a limit in the transit-time-limited gain-bandwidth product, GBW = 19 THz. The impulse response was modeled using a onedimensional deterministic model, which allowed a quantitative analysis of the data in terms of the average velocity of electrons and holes. The fitting of the data yielded a saturation of the electron and hole velocity of v e = 2.3 9 10 7 cm/s and v h = 1.0 9 10 7 cm/s at electric fields E > 1.5 kV/cm. The increase in rise time at high bias is consistent with the results of Monte Carlo simulations and can be partly explained by a reduction of the electron saturation velocity due to frequent impact ionization. Finally, the model was used to predict the bandwidth in diodes with shorter RC = 5 ps, giving BW = 16 GHz and BW = 21 GHz for x j = 4 lm and x j = 2 lm, respectively, for a gain of M = 100.

“…At present, the highest performance has been obtained at low temperatures, T = 77 K, in midwave Hg 1Àx Cd x Te detectors with x Cd = 0.35 to 0.3, with high gain at low reverse bias, low excess noise factor, and low dark currents; for example, Beck et al have reported equivalent input currents (shotnoise-limited input current corresponding to the output noise) of about I eq_in = 7 fA with a high operability, corresponding to a current density per pixel of J = 0.44 nA/cm 2 , estimated from a minimum value of NEPh min = 0.3 at a gain of M = 946 4 for k c = 4.2 lm cutoff wavelength in e-APDs at T = 77 K. In our detectors, we have shown that the equivalent input current can be as low as 1 fA in k c = 4.8 lm detectors at T = 77 K, for gains up to M = 100, corresponding to a rate of 6000 e/s. 12,13 The dark current levels obtained in MW APDs at T = 80 K, typically 100 fA, are low enough for most active imaging systems.…”

Section: Introductionmentioning

confidence: 98%

“…Several groups [1][2][3][4][5][6][7][8][9][10][11] have reported multiplication gains of 100 to 1000 for low values of reverse bias, around 10 V, associated with a quasideterministic multiplication yielding a conserved signal-to-noise ratio (SNR). These exceptional characteristics of HgCdTe APDs are due to exclusive impaction ionization of the electrons, which is why these devices have been termed electron-initiated avalanche photodiodes (e-APDs).…”

Section: Introductionmentioning

confidence: 99%

High-Operating-Temperature HgCdTe Avalanche Photodiodes

Rothman

Baier

Ballet

et al. 2009

In this communication we report the first results of electro-optical characterization of planar heterostructure HgCdTe avalanche photodiodes (APDs), which enables the operation of APDs at high gain, at low bias, and with low dark current and/or at high operating temperature (HOT). The APD is based on a heterostructure in which the photons are detected in a wide-bandgap layer, and the photoelectrons are amplified in a vertical junction in a confined narrow-gap layer. The dark diffusion current and thermal background sensitivity of the device are limited by using a thin narrow-band-gap amplification layer. In addition, the defect-limited dark current is also expected to be reduced due to the reduced volume of the narrow-band-gap depletion layer. The electro-optical performance was characterized at T = 80 K and T = 200 K for two devices with a nominal thickness of the amplification layer of w = 100 nm and 500 nm, realized in x Cd = 0.3 Hg-vacancy-doped layers grown by molecular-beam epitaxy (MBE). The measurements show an average gain of hMi = 10 at a reverse bias of 5 V, which is slightly reduced compared with a conventional APD with x Cd = 0.3. The thermal diffusion current measured at low reverse bias, V b = 0.1 V, and at T = 200 K is about 0.1 mA/cm 2 to 0.3 mA/cm 2 , which is a factor of 50 lower than standard x Cd = 0.3 n-on-p APDs. The quantum efficiency due to absorption in the gain layer is high (QE peak > 30%), although no antireflecting coating was used, indicating that the device can also be used for high-operating-temperature thermal detection.