## hbtex08.in : InP/InGaAs/InP Double HBT with varying doping profile

Requires: Blaze

Minimum Versions: Atlas 5.28.1.R

In this example a DHBT structure based on the InP / InGaAs material system is constructed using Atlas. The DHBT is then electrically tested, and properties that characterise the device's DC and high frequency performance are calculated and presented. The DC performance is shown through a gummel plot, and the DC current gain is calculated using the functions property in TonyPlot. The AC performance is evaluated via the cutoff frequency ft, as well as the maximum oscillation frequency fmax. The cutoff frequency is defined as the frequency at which the magnitude of AC current gain ( i.e. h21), decreases to unity. It is important to note that the transistor is connected in common-emitter configuration for this calculation. The maximum oscillation frequency fmax is the frequency at which the unilateral power gain of the transistor tends to unity. The unilateral power gain effectively represents the maximum power gain achievable by the transistor. These properties can be improved though appropriate use of heterostructures, stoichiometry and doping to lower collective resistance, epitaxial strain as well as several other properties, all of which are incorporated within HBTs and indeed DHBTs offering superior performance to BJTs.

The superior performance encountered with HBTs and DHBTs is mainly due to the presence of a quantum well in the emitter / base junction arising through the use of two materials of different band gap. In this example InP / In(0.53)Ga(0.47)As have been used. The quantum well stops back injection of holes from the base into the emitter which will reduce the base current and consequently increase the current gain. The quantum well will also permit the base doping to be increased which will lower the resistance encountered within the base and reduce the transit time for electrons thus increasing frequency performance. By adding a second heterostructure within the collector / base region (i.e. In(0.53)Ga(0.47)As / InP) epitaxial relationships are improved throughout the structural growth with an overall improvement in device performance.

Another technique to improve a device's performance is to use a graded doping profile. This will aid in controlling electric fields concomitant with depletion regions and will improve breakdown characteristics. This example demonstrates this ability by importing doping profiles previously specified in an ASCII text editor. These files are called upon during the construction stage and the doping profiles will be replicated accordingly. In this example the files used are ** hbtex08_n.dat ** and ** hbtex08_p.dat ** for n and p type doping respectively. The user can simply create an ASCII text file having two columns. The left column specifies the depth location and the right column specifies the concentration at that location.

An example would be:

** 0.0 1e16**

** 1.0 1e20**

** 1.001 0.0**

** 2.0 0.0**

** ( Must put a carriage return here )**

As this is an ASCII file, a carriage return must be placed at the end of the file. To use this file would require the commands:

doping (specify type) ascii infile=(filename)

It is also noted that interpolation is used between specified locations. Consequently the doping profile must be set to zero through certain locations if so desired. Otherwise an interpolated value will be used until the end of the device is encountered. This is demonstated in the above example.

The accuracy of the simulations is also improved by the use of Atlas-Interpreter mobility models for the materials. The models are based on "Empirical low-field mobility model for III-V compounds applicable in device simulation codes", M. Sotoodeh, A. H. Khalid, and A. A. Rezazadeh, J. Appl. Phys., 87, 2890 (2000).

To load and run this example, select the ** Load** button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the ** Run** button in DeckBuild to execute the example.

### Additional Info:

# Input Deck

# (c) Silvaco Inc., 2019 # An example of a double hetrostructure bipolar transitor. # The device is built using Atlas and incorporates doping # profiles sepecified by external ASCII files. go atlas mesh x.mesh loc=0.0 spac=0.05 x.mesh loc=0.3 spac=0.05 x.mesh loc=0.6 spac=0.05 x.mesh loc=1.0 spac=0.05 y.mesh loc=0.0 spac=0.02 y.mesh loc=0.048 spac=0.01 y.mesh loc=0.05 spac=0.01 y.mesh loc=0.052 spac=0.01 y.mesh loc=0.06 spac=0.01 y.mesh loc=0.145 spac=0.01 y.mesh loc=0.15 spac=0.01 y.mesh loc=0.151 spac=0.005 y.mesh loc=0.18 spac=0.01 y.mesh loc=0.19 spac=0.01 y.mesh loc=0.2 spac=0.01 y.mesh loc=0.21 spac=0.002 y.mesh loc=0.2199 spac=0.0001 y.mesh loc=0.22 spac=0.005 y.mesh loc=0.2201 spac=0.0001 y.mesh loc=0.23 spac=0.005 y.mesh loc=0.26 spac=0.01 y.mesh loc=0.29 spac=0.005 y.mesh loc=0.2999 spac=0.0001 y.mesh loc=0.3 spac=0.05 y.mesh loc=0.301 spac=0.001 y.mesh loc=0.31 spac=0.005 y.mesh loc=0.32 spac=0.005 y.mesh loc=0.34 spac=0.05 y.mesh loc=0.7 spac=0.03 y.mesh loc=0.72 spac=0.005 y.mesh loc=0.721 spac=0.005 y.mesh loc=0.725 spac=0.01 y.mesh loc=1.0 spac=0.07 region num=1 material=oxide region num=2 material=InGaAs x.min=0.0 x.max=0.3 y.min=0.0 y.max=0.15 x.comp=0.47 region num=3 material=InP x.min=0.0 x.max=0.3 y.min=0.15 y.max=0.22 region num=4 material=InGaAs x.min=0.0 x.max=0.6 y.min=0.22 y.max=0.3 x.comp=0.47 region num=5 material=InP x.min=0.0 x.max=1.0 y.min=0.3 y.max=1.0 electrode num=1 name=emitter x.min=0.0 x.max=0.3 y.min=0.0 y.max=0.0 electrode num=2 name=base x.min=0.45 x.max=0.6 y.min=0.22 y.max=0.22 electrode num=3 name=collector bottom # ######################## # Here two ASCII files are called to specify the doping properties. # hbtex08_n will provide n type doping and hbtex08_p will provide # p type doping. Each file can be viewed by selecting the file # name i.e. hbtex08_p and then pulling down the tool menu in tonyplot # and selecting TextEditor whilst the file name is still highlighted. # By performing a vertical cutline through the structure i.e hbtex08.str # the doping profiles can be easily viewed. doping x.min=0.0 x.max=1.0 y.min=0.0 y.max=1.0 n.type ascii infile=hbtex08_n.dat doping x.min=0.0 x.max=1.0 y.min=0.0 y.max=1.0 p.type ascii infile=hbtex08_p.dat mobility material=InP f.conmun=hbtex08_InP_skr.lib f.conmup=hbtex08_InP_skr.lib mobility material=InGaAs f.conmun=hbtex08_InGaAs_skr.lib f.conmup=hbtex08_InGaAs_skr.lib model fermi print cubic35 method climit=1e-4 output band.param con.band val.band e.mob h.mob flowlines u.srh u.auger solve init solve previous save outf=hbtex08.str tonyplot hbtex08.str -set hbtex08_doping.set #quit # NB. # v3 means a voltage on electrode 3 which is the collector. # v2 means a voltage on electrode 2 which is the base. solve v3=0.0001 solve v3=0.001 solve v3=0.01 solve v3=0.1 solve v3=2 solve v2=0.0001 solve v2=0.001 solve v2=0.01 solve v2=0.1 solve vstep=0.05 vfinal=0.4 electrode=2 log outf=hbtex08_IV.log solve solve vstep=0.05 vfinal=1.5 electrode=2 save outfile=hbtex08_IV.str tonyplot hbtex08_IV.str -set hbtex08_nconc.set tonyplot hbtex08_IV.log -set hbtex08_gummel.set tonyplot hbtex08_IV.log -set hbtex08_IV_dccurrentgain.set extract init infile="hbtex08_IV.log" extract name="Ic" y.val from curve(v."base",i."collector") where x.val=1.5 extract name="Ib" y.val from curve(v."base",i."base") where x.val=1.5 extract name="betamax" $Ic/$Ib #quit # Frequency analysis go atlas mesh infile=hbtex08.str mobility material=InP f.conmun=hbtex08_InP_skr.lib f.conmup=hbtex08_InP_skr.lib mobility material=InGaAs f.conmun=hbtex08_InGaAs_skr.lib f.conmup=hbtex08_InGaAs_skr.lib model fermi print cubic35 method climit=1e-4 output band.param con.band val.band load infile=hbtex08.str master solve previous solve v3=0.0001 ac freq=1e6 solve v3=0.001 ac freq=1e6 solve v3=0.01 ac freq=1e6 solve v3=0.1 ac freq=1e6 solve v3=0.5 ac freq=1e6 solve v3=0.75 ac freq=1e6 solve v3=1.0 ac freq=1e6 solve v2=0.0001 ac freq=1e6 solve v2=0.001 ac freq=1e6 solve v2=0.01 ac freq=1e6 solve v2=0.1 ac freq=1e6 solve v2=0.5 ac freq=1e6 solve v2=0.75 ac freq=1e6 solve v2=1.0 ac freq=1e6 log outf=hbtex08_freq.log gains inport=base outport=collector width=50 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac \ freq=1 fstep=10 nfstep=7 mult.freq solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=2e7 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=4e7 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=6e7 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=1e8 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=2e8 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=4e8 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=1e9 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=2.5e9 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=3.5e9 solve v2=1.0 v3=1.0 vstep=0.025 electrode=23 ac freq=2.2e10 tonyplot hbtex08_freq.log -set hbtex08_freq_accurrentgain.set tonyplot hbtex08_freq.log -set hbtex08_freq_unilateralpowergain.set quit