Mobility dependence of the temperature during of the growth Original Research Article Journal of Chemistry and Materials Research Vol. 1 (3), 2014, 56–59 Zehor Allam *, Abdelkader Hamdoune, Chahrazed Boudaoud, Aicha Soufi

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Journal of Chemistry and Materials Research
Vol. 1 (3), 2014, 5659
JCMR
Journal of Chemistry and
Materials Research
ORICPublications
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Original Research
Mobility dependence of the temperature during of the growth
Zehor Allam, Abdelkader Hamdoune, Chahrazed Boudaoud, Aicha Soufi
Unity of Research “Materials and Renewable Energies”, Faculty of Science, University of Abou-bekr Belkaid
Received 21 July 2014; received in revised form 18 August 2014; accepted 24 August 2014
Abstract
Development of wide-band gap III‒nitride semiconductors has been a subject of intense focus since the 1990s, primarily driven by the quest for
blue lasers and high-brightness light-emitting diodes (LEDs). In parallel, III‒nitrides have been studied extensively for use in ultraviolet (UV)
photodetectors because they offer intrinsic visible- or solar-blind detection, which would eliminate the need for expensive and
efficiency‒limiting optical filters to remove out‒of‒band visible or solar photons. Such detectors would be well suited for numerous
applications in the defense, commercial, and scientific arenas, including covert space-to-space communications, early missile-threat detection,
chemical and biological threat detection and spectroscopy, flame detection and monitoring, UV environmental monitoring, and UV astronomy.
In this paper, we consider an AlGaN/Si photodetector. We use ATLAS developed by International SILVACO‒TCAD for simulating. We
simulate the mobility dependence of the temperature and the current dependence of the temperature.
Keywords: Mobility of AlGaN; Atlas Simulation;UV Photodetector.
1. Introduction
Applications photodetectors are attracted considerable
interest in optoelectronic field especially in the domain of
communication [1]. MSM (metal‒semiconductor‒metal) phot-
odetectors are usually very used for ultraviolet detection. The
Schottky contact is characterized by a significant barrier betw-
een the metal and the semiconductor provides a high perfor-
mance [2]. Effective robust UV detector with a low cost, able
to work in all circumstances easy installed in various electro-
nic instruments. These photodetectors has different applicat-
ions in fire detection, missile guidance ... [3].
The column III nitride has a strong interest in UV detection
was considered very promising for device applications in
ultraviolet to blue and ultraviolet wave lengths in the same way
that his great success As‒based and p‒based were used for
infrared, red and yellow wave lengths. As members of the
family of III‒V nitrides, AlN, GaN, InN and their alloys are
materials broadband and can crystallize in both wurtzite and
* Corresponding author. Tel.: +21343285686; fax: +21343285685.
E-mail address: zh1344@yahoo.fr (Z. Allam).
All rights reserved. No part of contents of this paper may be reproduced or
transmitted in any form or by any means without the written permission of
ORIC Publications, www.oricpub.com.
zinc‒blende polytypes [4]. The quality of the Schottky contact
is presents an important factor for achieving high device
performance [5].
Detecting UV radiation between the wavelengths 200 nm
to 280 nm is very important in the atmosphere. Therefore, the
solar blind (200‒280 nm) UV photodetector would be more
practical and necessary [6].
2. Modeling Process
ATLAS predicts the electrical characteristics of the
proposed physical structures, can simulate the electrical
transport in two dimensions. These simulations can be made
much cheaper and faster than physical experimentation and
can provide information ultraviolet photodetector that is
difficult or impossible to measure [7].
The proposed structure of AlGaN/Si photodetectors is
shown in Fig. 1; it was simulated using ATHENA and ATLAS
in SILVACO TCAD device simulation.
ATHENA was employed to define the device structure in
two dimensions (x‒and y‒axis). ATLAS was used to evaluate
the photo-device characteristics with and without illumination.
Since LAS does not contain all necessary properties of AlN
and GaN‒based material, we had to calculate and enter the
following parameters in the simulation software.

2. Z. Allam et al. / Journal of Chemistry and Materials Research 1 (2014) 56–59 57
Fig. 1. Growth of AlGaN with thickness of 0.2μm onto silicon
substrate in the dark.
The energy band diagram has been simulated using
BLAZE tool which is interfaced with ATLAS and which is a
general purpose 2D device simulator for III–V, II–VI
materials, and devices with position dependent band structure
(i.e., heterojunctions) [8]. BLAZE takes into account the
effects of the position of the band structure depending on the
changes in the charge transport equations.
The detector is based 0.2 μm thick of AlGaN epitaxial
layers grown on silicon substrate by metalorganic chemical
vapor deposition (MOCVD) [9]. And composed of a thick
layer of AlGaN equal to 0.1 μm at a temperature less than
1050 K this layer is of type N unintentionally doped, the last
layer 0.1 µm thick achieve under temperature (1100 K) this is
undoped AlGaN interlayer and the substrat of Silicon with 0.3
µm thick. With 250 nm of conductor film was then deposited
on the sample by RF magnetron sputtering.
The numerical simulation of AlGaN photodetector has
been carried out for non‒degenerate semiconductor and
parabolic shape of conduction band. The simulation involves
solution of five decoupled equations using Newton’s iteration
technique.
The Fermi–Dirac statistic for parabolic shape of conduc-
tion band has been taken in all the calculations of carrier and
doping densities.
For the simulation of I‒V current associated with AlGaN
photodetector; radiative recombination (Rc), recombination
rate (RSRH), Auger recombination (RAuger), and surface
recombination (Rsurf) rates, are modeled as:
2
( )opt opt
c c i
R C pn n  (1)
2
exp exp
i
SRH
t t
pO i nO i
pn n
R
E E
n n p n
kT kT
 


     
      
            
(2)
2 22 2
( ) ( )Auger n pi iR C n C np nn p pn    (3)
2
exp exp
i
surf
eff efft t
p i n i
pn n
R
E E
n n p n
kT kT
 


     
      
            
(4)
here opt
cC is the capture rate of carriers; Cn and Cp are Auger
coefficients for electrons and holes respectively; n and p are
equilibrium electron and hole concentration, Et is energy level
of trap; ni is intrinsic carrier concentration; 0n and 0p are
SRH lifetime of electrons and holes respectively; eff
n and
eff
p are effective life times of electrons and holes
respectively [10].
3. Results and discussion
The simulated results were obtained by developing
program in DECKBUILD window interfaced with ATLAS for
Al0.2Ga0.8N/Si photodetector, at 300 K. Instead of the graded
doping, the numerical model assumes a uniform doping
profile. Once the physical structure of photodetector is built in
ATLAS, the properties of the material used in device must be
defined. A minimum set of material properties data includes
bandgap, dielectric constant, and electron affinity, densities of
conduction and valence band states, electron mobility, and
hole mobility.
Mobility is a very significant characteristic of material, bec-
ause it translates the capacity which has the carriers to move in
material. It is thus a factor determining for the devices. This is
very significant for fields like optoelectronics, or telecommu-
nications. According to the definition of mobility, electronic
transport depends primarily on two parameters: effective mass
of the electrons and the frequency of the interactions with the
crystal lattice. However, any modification in this network, like
the rise in the temperature or doping, will modify the mobility
of the carriers generally noted µ (see Fig. 2).
Fig. 2. Mobility dependence of the temperature in AlGaN/Si
photodetector.

3. 58 Z. Allam et al. / Journal of Chemistry and Materials Research 1 (2014) 56–59
Fig. 3. Current dependence of the temperature in AlGaN/Si
photodetector.
One thus notes that the more the temperature of material is
raised, the more mobility will fall, which it case of all the
semiconductors.
The carrier mobility is related to the mean free path
without collision in the semiconductor; any change in the
crystal lattice causes a change in mobility.
Indeed, the increase in temperature creates disturbances in
the crystal and affects mobility.
In the temperature range from 110 to 1000 K, the electron
mobility decreases from 490 to 100 cm2
/Vs.
We note that the increase in mobility with temperature is
mainly limited by the diffusion of ionized impurities. When the
temperature increases, the effect of the carrier velocity
increase and thus reduce broadcasts with ionized impurities.
Mobility is limited by scattering with acoustic phonons
through the potential associated with the deformation of the
piezoelectric array and fields. The piezoelectric effect does not
operate a role in the diffusion of electrons in the field of low
temperatures. For high temperatures, there is a saturation
phenomenon when mobility is mainly limited by diffusion with
polar optical phonons.
The temperature of the substrate must be sufficiently high
to allow diffusion of the atoms on the sufficiently low surface
but to allow the incorporation of germanium and aluminum.
The growth is carried out in mode of germanium excess and
aluminum with segregation of one full‒course of If on the face
of growth.
The AlGaN/Si structure the current gives a maximum value
at 280 K equal 1.2 A (see Fig. 3).
In the interface metal /semiconductor is a potential barrier
for electrons is the difference in work function between the
metal and the semiconductor.
This causes the formation of heterojunction a potential well
in the small‒gap material in which electrons from the donor
layer are transferred and accumulated.
Fig. 4. AlGaN/Si internal potential.
The heterojunction is characterized by the discontinuity of
the energy of the conduction band between the two materials,
plus the value of the energy of the conduction band is high, the
electron transfer from the donor layer to the channel will be
better. In addition, over the material of the channel will be
small gap, the transport properties (speed, mobility) will be
better (see Fig. 4).
4. CONCLUSION
 In this paper, we studied an AlGaN/Si photodetector
device. Modeling and simulation were performed by
using ATLAS‒TCAD simulator.
 In the temperature range from 110 to 1000 K, the
electron mobility decreases. The of growth of AlGaN
under silicon substrate give a maximum value of
current gives at 280 K equal 1.2 A.
 The simulation and modeling described in this work
can be used for optimizing the existing ultraviolet
detectors and developing new devices.
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