Актуальные проблемы радиофизики АПР 2019 Сборник …

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8-я Международная научно-практическая конференция

Актуальные проблемы радиофизикиАПР 2019

Сборник трудов конференции

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РОССИЙСКИЙ ФОНД

ФУНДАМЕНТАЛЬНЫХ ССЛЕДОВАНИЙ

1-4 октября 2019 года

г. Томск

Parameters comparison between quantum dot infrared detectors of Ge/Si and HgCdTe

detectors

Douhan Rahaf M.H.

Kokhanenko Andrey Pavlovich, Lozovoy Kirill Alexandrovich

National Research Tomsk State University, Tomsk, Russia

E-mail: [email protected]

The work discusses infrared photodetectors with quantum dots of germanium on silicon. The calculation of

certain characteristics of detectors such as: dark current and detectability in three different modes with special

interest in the size of the quantum dots.

The information society requires innovative devices with new or significantly improved characteristics

compared to those currently available. There is a general opinion that nanoelectronic devices will be the basis of new

devices that will replace microelectronic ones. Over the past 50 years, semiconductors have become an essen- tial

material for the manufacture of electronic and optoelectronic devices. Although the first transistor was made from

Germanium (Ge), today one semiconductor, in particular silicon (Si), dominates the production of transistors and

integrated circuits. Both, Si and Ge, are elementary semiconductors of the fourth group of the periodic table.

The discovery of the quantum Hall effect in 1980, led to the search for new electronic and optoelectronic

devices based on low-dimensional semiconductor structures such as two -, one - and even zero-dimensional systems.

In these structures, quantum mechanical effects become significant when the typical length of 100 nm or less is

reached. Currently, researchers around the world are seeking to implement quantum wires and quantum dot lasers, as

well as devices based on one-electron tunneling [1].

In this work, the main parameters of quantum dot infrared photodetectors made from quantum dots of ger-

manium on silicon are calculated and the results are highlighted to reveal the differences and special attention were

paid to the effect of the quantum dots size. It is expected that the photodetectors with quantum dots can provide bet-

ter performance, namely higher operating temperature (due to the large lifetime of carriers), low dark current and high

coefficient of photoelectric gain.

In order to determine a good photodetector, we should pay attention to several parameters such as detectivi-

ty, noise, the dark current and others.

Detectivity of a photodetector reflects the signal to noise ratio and we use the following formula to calcu-

late it [2]:

(1)

Here η- is the external quantum efficiency of the detector, q- is the electron charge, h- is the Planck con-

stant, ν- is the incident radiation frequency,

G- is the rate of thermal generation of charge carriers determined by the expression [2]:

(2)

Where q- is the electron charge, - the standard deviation in energy for the shape of the Gauss line (the

position spread of the main energy level - kt), D- is the surface density of quantum dots, t- the total thickness of the

quantum dots layer, A- is the maximum absorption coefficient, n1 is the surface concentration of electrons in the

ground state of a quantum dot, F- Fermi function. τ - lifetime of charge carriers.

The main sources of noise in photodetectors with quantum dots are the noise of generation-recombination,

thermal noise and noise caused by fluctuations of background radiation [3].

Therefore, the total noise current of a photodetector with quantum dots in the General case can be written

as:

(3)

АПР 2019______________________________________________________________________________________________________Квантовая электроника и фотоника

1-4 октября 2019, Томск 389

mailto:[email protected]

Where is the noise current caused by the generation- recombination, is the thermal noise current and

is the noise current due to fluctuations of background radiation [3].

The noise current limited by thermal generation is determined by [2]:

(4)

In turn, for a photodetector based on n-type HgCdTe material, it is assumed that the lifetime of non- primary

charge carriers will be limited by the lifetime of the auger recombination for the native material and the thermal

generation rate in this case can be set as follows [2]:

(5)

The dark current of the photodetector is the current caused by sources other than the photocurrent due to the

excitation of charge carriers by the incident signal radiation. It is known that in photodetectors with quantum dots the

main source of dark current is the excitation of carriers due to thermal emission and tunneling in the pres- ence of an

electric field. In this case, the dark current density can be estimated by the following expression [4]:

(6)

where q- is the electron charge, m*- is the effective mass of the carrier in the barrier layer, - is the Boltzmann

constant, h is the Planck constant, is the activation energy, F is the applied electric field, µ is the mobility and vs

is the maximum velocity of the carriers.

The last term in the expression (3) is a noise current that appears due to fluctuations according to charge

carriers that are excited by background radiation. In General, this current can be written as follows [5]:

(7)

Where - the flux density of the background photons.

The limiting characteristics of infrared photodetectors correspond to their mode of limiting the fluctuations

of the background radiation, or in the limit of photon noise, this mode called BLIP-mode (background limited per-

formance). This performance mode is very convenient for comparing different types of photodetectors, so we made

our calculations depending on the it and we observed that an infrared photodetector from germanium quantum dots

on silicon has the following characteristics:

In the thermal generation of charge carrier mode:

It should be noted that at low temperatures, the dark current in the structures with quantum dots is higher

than HgCdTe photodetectors. However, at high temperatures the dark current is less as shown in Fig.1. Also notic-

ing the dark current when σ = 10 and when σ = 100 it’s about an order difference in the performance and comparing

the results with the HgCdTe photodetectors give us the same difference and more in cases where σ is smaller.

The detectivity of QDIP compared to HgCdTe photodetectors is better only in the case of high temperature

conditions as shown in Fig.2. Also, we can notice that in low temperatures the HgCdTe detectors have better detec-

tivity but while the temperature increases the detectivity of these detectors highly decreased, unlike the Si/Ge quan-

tum dots photodetectors the decreasing of their detectivity is acceptable. Also, it has been noticed that in QDIP the

quantum dot size is very important the smaller the size of a quantum dot the better the detectivity will be.

It is seen that at high operating temperatures (150-300 K) and a high degree of homogeneity of the Islands,

the value of the detectivity for photodetectors on Ge/Si quantum dots in the mode of limiting the thermal generation

of carriers can be two orders of magnitude higher than the detectivity for HgCdTe detectors (Fig.2)



Fig.1 Dark current caused by thermal generation for

photodetectors based on HgCdTe and QDIP with dif-

ferent degree of inhomogeneity of Islands σ.

Fig.2 Detectivity caused by thermal generation for

photodetectors based on HgCdTe and QDIP with

different degree of inhomogeneity of Islands σ.

In generation-recombination noise mode the dark current of photodetector is very dependent on the operat-

ing temperature. In addition, the density of the dark current in the region of small bias voltages increases sharply with

the growth of the applied electric field, but in the region of large bias voltages, the dark current increases more

smoothly. The increase in the inhomogeneity of quantum dots in size significantly impairs the performance of the

photodetector at quantum dots as seen in (Fig. 3).

Fig.3 Dark current density in generation-

recombination noise mode for QDIP as a function of

the activation energy σE at U = 5 V and different op-

erating temperatures T

Fig.4 Dark current density in generation-

recombination noise mode for QDIP as a func-

tion of the activation energy E0, n at σE = 30

MeV, U = 5 V and different operating tempera-

tures T σ.

In background radiation mode (BLIP mode) is implemented at T = 110 K and below, which is in agreement

with the experimental data from [6] (Fig.5).



Fig.5 Dark current density caused by generation-

recombination noise and background noise, for a photodetector based on germanium quantum dots in silicon at σE = 30 MeV and

different voltages.

REFERENCES

[1] Holger T Grahn // Introduction to semiconductor physics, Berlin,1999, P.183.

[2] Phillips J.// Evaluation of the fundamental properties of quantum dot infrared detectors // J. Appl. Phys. – 2002. – V. 91. –

№ 7. – P. 4590-4594.

[3] Rogalski A.// Infrared Detectors. – Boca Raton: CRC Press, 2011. P: 876.

[4] Liu G., Zhang J., Wang L.// Dark current model and characteristics of quantum dot infrared photodetectors // Infrared

Phys-ics & Technology. – 2015. – V. 73. – P. 36-40.

[5] Keyes R. J., Cruz P. V., Patel E. G., long, D., Zwicker G. R., Milton, A. F., M. K. Teich// Photodetectors of visible and IR

ranges. – Moscow: Radio and communication, 1985. –P. 328.

[6] Yakimova . And. // Autometry. – 2013. – Vol. 49. – P. 57-67.



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Актуальные проблемы радиофизики АПР 2019 Сборник …