HgCdTe MWIR Back-Illuminated Electron-Initiated Avalanche Photodiode Arrays

The response time of front-sided illuminated n-on-p Hg 0.7 Cd 0.3 Te electron avalanche photodiodes (e-APDs) at T = 77 K was studied using impulse response measurements at k = 1.55 lm. We measured typical rise and fall times of 50 ps and 800 ps, respectively, at gains of M % 100, and a record gainbandwidth (GBW) product of GBW = 1.1 THz at M = 2800. Experiments as a function of the collection width have shown that the fall time is strongly limited by diffusion. Variable-gain measurements showed that the impulse response is first-order sensitive to the level of the output amplitude. Only a slight increase in the rise time and the fall time was observed with the gain at constant output amplitude, which is consistent with a strongly dominant electron multiplication. Comparisons of the experimental results with Silvaco finite element simulations confirmed the diffusion limitation of the response time and allowed the illustration of the transit time and RC effects.

Section: Introductionsupporting

confidence: 64%

Impulse Response Time Measurements in Hg0.7Cd0.3Te MWIR Avalanche Photodiodes

Perrais

Rothman

Destéfanis

et al. 2008

“…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.

“…Spot scan data on back-side illuminated planar e-APDs were first reported by Reine et al 3 Here we present spot scan data on top-side illuminated MWIR cylindrical APDs operating at 77 K.…”

Section: Spot Scan Measurementsmentioning

confidence: 69%

“…[1][2][3] Photon-level sensitivity has been demonstrated at DRS with high noise equivalent photon operabilities in 128 9 128 4 and 320 9 240 5 gated arrays using e-APD in the p-around-n, high-density vertically integrated photodiode (HDVIP Ò ) cylindrical diode configuration. Given this performance, there is increasing interest in using the e-APD in a variety of applications.…”

Section: Introductionmentioning

confidence: 99%

Performance and Modeling of the MWIR HgCdTe Electron Avalanche Photodiode

Beck¹,

Scritchfield²,

Sullivan³

et al. 2009

The operation of the mid-wave infrared (MWIR) HgCdTe cylindrical electron injection avalanche photodiode (e-APD) is described. The measured gain and excess noise factor are related to the collection region fill factor. A twodimensional diffusion model calculates the time-dependent response and steady-state pixel point spread function for cylindrical diodes, and predicts bandwidths near 1 GHz for small geometries. A 2 lm diameter spot scan system was developed for point spread function and crosstalk measurements at 80 K. An electron diffusion length of 13.4 lm was extracted from spot scan data. Bandwidth data are shown that indicate bandwidths in excess of 300 MHz for small unit cells geometries. Dark current data, at high gain levels, indicate an effective gain normalized dark density count as low as 1000 counts/ls/cm 2 at an APD gain of 444. A junction doping profile was determined from capacitance-voltage data. Spectral response data shows a gain-independent characteristic.