G4CMP -- Geant4 add-on framework for phonon and charge-carrier physics

R. Agnese, D. Brandt, M. Kelsey, P. Redl, I Ataee Langroudy

This package provide a collection of particle types, physics processes, and supporting utilities to simulate a limited set of solid-state physics processes in Geant4. Developed for the low-temperature community, the package support production and propagation of acoustic phonons and electron-hole pairs through solid crystals such as germanium.

Software Licenses

This product includes software developed by Members of the Geant4 Collaboration ( http://cern.ch/geant4 ). A copy of the Geant4 license is included at G4CMP/Geant4_LICENSE.html.

This product ships an unaltered copy of Qhull source code. This is so that we may compile and link the code in an unsupported way. The Qhull license is included at G4CMP/qhull-2012.1/COPYING.txt.

The original parts of the product are licensed under the GNU General Public License version 3 or (at your discretion) any later version. The full license can be found at G4CMP/LICENSE.

User Environment

Users must have a recent (10.4 through 10.7) version of GEANT4 installed and configured (via GEANT4's bin/geant4.sh or bin/geant4.csh. See GEANT4's documentation for further instructions.).

NOTE The release of Geant4 Version 11 introduced substantial and breaking changes to many Geant4 interface classes. We are maintaining G4CMP under ==Geant4 Version 10== (through 10.7) to ensure compatibility with our major experimental users.

Add the G4CMP environment variables using the g4cmp_env.csh or ...sh scripts found in the G4CMP installation directory (see below for build and installation procedures):

source g4cmp_env.csh		# For CSH/TCSH users
. g4cmp_env.sh			# For SH/BASH users

This must be done before building or running executables.

G4CMP is only configured for use on Linux and MacOSX platforms. A minimum configuration requires a recent enough version of GCC or Clang to support the C++11 standard.

Several configuration parameters are available through environment variables and macro commands, as listed below. Most of these affect charge carrier propagation and related processes. Because G4CMP is in a very active development state, do not expect this table to stay up-to-date. Rather, developers should check the source code in G4CMP/library/src/G4CMPConfigManager.cc and G4CMP/library/src/G4CMPConfigMessenger.cc to see what is available.

Environment variable	Macro command	Value/action
G4LATTICEDATA [P1:P2...]	/g4cmp/LatticeData [P1:P2:...]	Paths with lattice configs
G4CMP_DEBUG	/g4cmp/verbose [L] >0:	Enable diagnostic messages
G4CMP_CLEARANCE [L]	/g4cmp/clearance [L] mm	Minimum distance of tracks from boundaries
G4CMP_VOLTAGE [V]	/g4cmp/voltage [V] volt !=0:	Apply uniform +Z voltage
G4CMP_EPOT_FILE [F]	/g4cmp/EPotFile [F] V=0:	Read mesh field file "F"
G4CMP_EPOT_SCALE [F]	/g4cmp/scaleEPot [M] V=0:	Scale the potentials in EPotFile by factor m
G4CMP_MIN_STEP [S]	/g4cmp/minimumStep [S] S>0:	Force minimum step S*L0
G4CMP_EH_BOUNCES [N]	/g4cmp/chargeBounces [N]	Maximum e/h reflections
G4CMP_PHON_BOUNCES [N]	/g4cmp/phononBounces [N]	Maximum phonon reflections
G4CMP_MAKE_PHONONS [R]	/g4cmp/producePhonons [R]	Fraction of phonons from energy deposit
G4CMP_MAKE_CHARGES [R]	/g4cmp/produceCharges [R]	Fraction of charge pairs from energy deposit
G4CMP_LUKE_SAMPLE [R]	/g4cmp/sampleLuke [R]	Fraction of generated Luke phonons
G4CMP_MAX_LUKE [N]	/g4cmp/maxLukePhonons [N]	Soft maximum Luke phonons per event
G4CMP_SAMPLE_ENERGY [E]	/g4cmp/samplingEnergy [E] eV	Energy above which to downsample
G4CMP_COMBINE_STEPLEN [L]	/g4cmp/combiningStepLength [L] mm	Combine
hits below step length
G4CMP_EMIN_PHONONS [E]	/g4cmp/minEPhonons [E] eV	Minimum energy to track phonons
G4CMP_EMIN_CHARGES [E]	/g4cmp/minECharges [E] eV	Minimum energy to track charges
G4CMP_RECORD_EMIN	/grcmp/recordMinETracks [t|f]	Put below-minimum energy to killed track Edeposit
G4CMP_USE_KVSOLVER	/g4mcp/useKVsolver [t|f]	Use eigensolver for K-Vg mapping
G4CMP_FANO_ENABLED	/g4cmp/enableFanoStatistics [t|f]	Apply Fano statistics to input ionization
G4CMP_KAPLAN_KEEP	/g4cmp/kaplanKeepPhonons [t|f]	Reflect or iterate all phonons in KaplanQP
G4CMP_IV_RATE_MODEL	/g4cmp/IVRateModel [IVRate|Linear|Quadratic]	Select intervalley rate parametrization
G4CMP_ETRAPPING_MFP	/g4cmp/eTrappingMFP [L] mm	Mean free path for electron trapping
G4CMP_HTRAPPING_MFP	/g4cmp/hTrappingMFP [L] mm	Mean free path for charge hole trapping
G4CMP_EDTRAPION_MFP	/g4cmp/eDTrapIonizationMFP [L] mm	MFP for e-trap ionization by e-
G4CMP_EATRAPION_MFP	/g4cmp/eATrapIonizationMFP [L] mm	MFP for h-trap ionization by e-
G4CMP_HDTRAPION_MFP	/g4cmp/hDTrapIonizationMFP [L] mm	MFP for e-trap ionization by h+
G4CMP_HATRAPION_MFP	/g4cmp/hATrapIonizationMFP [L] mm	MFP for h-trap ionization by h+
G4CMP_TEMPERATURE	/g4cmp/temperature [T] K	Device/substrate/etc. temperature
G4CMP_NIEL_FUNCTION	/g4cmp/NIELPartition [LewinSmith|Lindhard]	Select NIEL partitioning function
G4CMP_CHARGE_CLOUD	/g4cmp/createChargeCloud [t|f]	Create charges in sphere around location
G4CMP_MILLER_H	/g4cmp/orientation [h] [k] [l]	Miller indices for lattice orientation
G4CMP_MILLER_K
G4CMP_MILLER_L
G4CMP_HIT_FILE [F]	/g4cmp/HitsFile [F]	Write e/h hit locations to "F"

The default lattice orientation is to be aligned with the associated G4VSolid coordinate system. A different orientation can be specified by setting the Miller indices (hkl) with $G4CMP_MILLER_H, _K, and _L.

The environment variable $G4CMP_MAKE_CHARGES controls the rate (R) as a fraction of total interactions, at which electron-hole pairs are produced by energy partitioning. Secondaries will be produced with a track weight set to 1/R:

unsetenv G4CMP_MAKE_CHARGES     # No new charge pairs generated
setenv G4CMP_MAKE_CHARGES 1     # Generate e/h pair at every occurrence
setenv G4CMP_MAKE_CHARGES 0.001 # Generate e/h pair 1:1000 occurrences

When secondary phonons are not produced, the equivalent energy is recorded as non-ionizing energy loss (NIEL) on the track. Generating seconary phonons will significantly slow down the simulation.

The environment variable $G4CMP_MAKE_PHONONS controls the rate (R) as a fraction of total interactions, at which "primary" phonons are produced (by energy partitioning or recombination). Secondaries will be produced with a track weight set to 1/R:

unsetenv G4CMP_MAKE_PHONONS     # No secondary phonons generated
setenv G4CMP_MAKE_PHONONS 1     # Generate phonon at every occurrence
setenv G4CMP_MAKE_PHONONS 0.001 # Generate phonon 1:1000 occurrences

When primary phonons are not produced, the equivalent energy is recorded as non-ionizing energy loss (NIEL) on the track.

Secondary phonons may be produced either by downconversion of higher energy phonons, or by emission of Luke-Neganov phonons from charge carriers. Generating secondary phonons can significantly slow down the simulation, so the LukeScattering process has an analogous environment variable, $G4CMP_LUKE_SAMPLE, defined with rate (R) as above.

For simulations which generate primary phonons and charge carriers from Geant4 energy deposition (using G4CMPEnergyPartition), the above environment variables may be replaced with a sampling "energy scale," $G4CMP_SAMPLE_ENERGY. This parameter is applied to each energy deposit, and to ionization or NIEL energy separately. If the energy deposit is below the scale, then no biasing will be done (the scale factors will all be set to 1.). Above the energy scale setting, the scale factors will be set according to E_scale_/E_deposit_. In this mode, an additional sampling parameter, $G4CMP_MAX_LUKE, may be set. This sets an approximate maximum number of Luke-Neganov phonons to be produced per event; the default is about 10,000.

The parameter $G4CMP_COMBINE_STEPLEN (/g4cmp/combiningStepLength) specifies a minimum step length for individual G4CMPEnergyPartition hits. Shorter contiguous steps by a track will be consolidated into one hit, which will then be processed with sampling as described above. When combined with Geant4's built in secondary production cuts, this should improve runtime performance substantially.

For phonon propagation, a set of lookup tables to convert wavevector (phase velocity) direction to group velocity are provided in the lattice configuration file (see below). The environment variable $G4CMP_USE_KVSOLVER controls whether the eigenvalue solver should be used directly for these calculations, instead of the lookup tables. The eigensolver imposes a factor of three penalty in CPU time, with the benefit of maximum accuracy in phonon kinematics.

Three optional environment variables are used to configure the electric field across the germanium crystal. $G4CMP_VOLTAGE specifies the voltage across the crystal, used to generate a uniform electric field (no edge or corner effects) from the bottom to the top face. If the voltage is zero (the default), then $G4CMP_EPOT_FILE specifies the name of the mesh electric field field to be loaded for the g4cmpCharge test job. There is no default file.

For developers, there is a preprocessor flag (make G4CMP_DEBUG=1) which may be set before building the libraries. This variable will turn on some additional diagnostic output files which may be of interest.

Building the Package

G4CMP supports building itself with either GNU Make or CMake, and separately supports being linked into user applications with either GNU Make (via environment variable settings) or CMake.

Building with Make

Configure your Geant4 build environment using <g4dir>/share/Geant4-${VERSION}/geant4make/geant4make.csh or ...sh, then configure or G4CMP environment as described above with g4cmp_env.csh or ...sh.

After configuring your environment, build the G4CMP library with the command

make library

The libraries (libg4cmp.so and libqhull.so) will be written to your $G4WORKDIR/lib/$G4SYSTEM/ directory, just like any other Geant4 example or user code, and should be found automatically when linking an application.

If you want debugging symbols included with the G4CMP library, you need to build with the G4DEBUG environment or Make variable set:

export G4DEBUG=1

or setenv G4DEBUG 1 or make library G4DEBUG=1

If you want to enable additional diagnostics in some processes, including writing out statistics files, build with the G4CMP_DEBUG environment or Make variable set. Note that this is not compatible with running multiple worker threads.

export G4CMP_DEBUG=1

or setenv G4CMP_DEBUG 1 or make library G4CMP_DEBUG=1

If you want to enable "sanitizing" options with the library, to look for memory leaks, thread collisions etc., you may set the options G4CMP_USE_SANITIZER and G4CMP_SANITIZER_TYPE (default is "thread"):

export G4CMP_USE_SANITIZER=1

or setenv G4CMP_USE_SANITIZER 1 or make library G4CMP_USE_SANITIZER=1

NOTE: If your source directory was not cloned from GitHub (specifically, if it does not contain .git/) you may need to specify a version string for identify the G4CMP version at runtime. Use G4CMP_VERSION=X.Y.Z on the Make command line for this purpose. If .git/ is available, the option will be ignored.

Building with CMake

Create a build directory outside of the source tree, such as

mkdir /path/to/G4CMP/../G4CMP-build
cd /path/to/G4CMP-build

We must tell CMake where GEANT4 is installed. If you want only the library to be built, use the following command

cmake -DGeant4_DIR=/path/to/Geant4/lib64/Geant4-${VERSION} ../G4CMP

By default, CMake will install a software package under /usr/local. If you want to install to a local path, rather than system-wide, use the -DCMAKE_INSTALL_PREFIX=/path/to/install option.

If you want debugging symbols included with the G4CMP library, you need to include the -DCMAKE_BUILD_TYPE=Debug option.

If you want to enable additional diagnostics in some processes, including writing out statistics files, include the -DG4CMP_DEBUG=1 option. Note that this is not compatible with running multiple worker threads.

If you want to enable "sanitizing" options with the library, to look for memory leaks, thread collisions etc., you may set the options -DG4CMP_USE_SANITIZER=ON and (optionally) -DG4CMP_SANITIZER_TYPE=value (default is "thread", other values may be "memory", "address", or "leak"). If you do this, we recommend using the "Debug" build type.

NOTE: If your source directory was not cloned from GitHub (specifically, if it does not contain .git/) you may need to specify a version string for identify the G4CMP version at runtime. Use the -DG4CMP_VERSION=X.Y.Z option for this purpose. If .git/ is available, the option will be ignored.

If you want to copy the examples directories (see below) to the installation area, use the option -DINSTALL_EXAMPLES=ON (for all examples). Each example has been set up as a standalone "project" for CMake and can be configured via:

cmake -DGeant4_DIR=/path/to/Geant4/lib64/Geant4-${VERSION} -DINSTALL_EXAMPLES=ON ../G4CMP

Once you've configured the build with cmake and option flags, run the make command in the build directory

make

and transfer the successfully build libraries to your installation area

make install

Once the install step is completed, the /path/to/install/share/G4CMP/ directory will contain copies of the g4cmp_env.csh and ...sh scripts discussed above. These copies should be sourced in order to correctly locate the installed libraries and header files.

Linking user applications against G4CMP

G4CMP is an application library, which can be linked into a user's Geant4 application in order to provide phonon and charge carrier transport in crystals. Users must reference G4CMP in their application build in order to utilize these features.

After running one of the setup scripts mentioned above (g4cmp_env.csh or g4cmp_env.sh), several environment variables will be defined to support linking G4CMP into your applications:

Environment variable	Meaning	Value in Make build	Value in CMake build
G4CMPINSTALL	Path to g4cmp_env.* scripts		$CMAKE_INSTALL_PREFIX/share/G4CMP
G4CMPLIB	Directory containing libG4cmp.so	$G4WORKDIR/lib/$G4SYSTEM	$G4CMPINSTALL/lib
G4CMPINCLUDE	Path to library/include	$G4INSTALL/library/include	$CMAKE_INSTALL_PREFIX/include
G4LATTICEDATA	Path(s) to CrystalMaps	$G4INSTALL/CrystalMaps	$G4INSTALL/CrystalMaps

If you have a simple Makefile build system (GMake), the following two lines, or an appropriate variation on them, should be sufficient:

CXXFLAGS += -I$(G4CMPINCLUDE)
LDFLAGS += -L$(G4CMPLIB) -lG4cmp -lqhullcpp -lqhullstatic_p

These actions must occur before the Geant4 libraries and include directory are referenced (G4CMP includes modified versions of some toolkit code).

If you are using CMake to build your application, it should be sufficient to add the following two actions, before referencing Geant4:

find_package(G4CMP REQUIRED)
include(${G4CMP_USE_FILE})

Application Examples

In addition to the library, G4CMP is distributed with an examples directory containing three simple applications to demonstrate features of the library.

• The phonon example shows phonon transport and scattering, including downconversion and mode mixing, in a cylindrical crystal.

• The charge example shows electron and hole transport with NTL ("Luke") emission of phonons and intervalley scattering.

• The sensor example shows how to configure the geometry to collect and record phonon energy by absorption on superconducting TES-style surface sensors.

Users may copy any of the individual example directories to their own work area and adapt them as necessary, or use them as inspiration in developing a more complex experimental model application.

Building Examples In Situ

If the G4CMP libraries are being built with Make, any of the three demonstration programs (phonon, charge) may be built as a normal GEANT4 user application directly from the package top-level directory. Use the command

make examples

to build them all, or

make <name>

to build just one (where is the directory name of interest). The executables will be named g4cmpPhonon and g4cmpCharge, respectively, and will be written to $G4WORKDIR/bin/$G4SYSTEM/.

Building Examples With CMake

Each example has been set up as a standalone "project" for CMake. Copy the example directory, and use cmake with -D options to set up and build the example.

Versioning Information

G4CMP provides somewhat limited access to version information at run time.

Since the package is primarily distributed through GitHub, users can query the state of their local clone at the command line, using git describe to get back a string such as "G4CMP-190" or "g4cmp-V07-02-02".

For static (tar-ball) distributions, the Git state at the time the tar-ball was created (using the make dist target) will be stored in a file named .g4cmp-version. This same file will be created as part of the build process using either Make or CMake (see above).

At runtime, the version string will be available through a call to G4CMPConfigManager::Version().

Defining the Crystal Dynamics

In a user's application, each active G4CMP material (e.g., germanium crystals or diamonds) must have a collection of dynamical parameters defined. These parameters are used by the phonon and charge-carrier processes to know how to create, propagate, and scatter the particles through the crystal.

Each material's parameters are stored in a subdirectory under CrystalMaps; the environment variable used to search for these material configuration files, $G4LATTICEDATA, points to this directory by default. Additional paths can be included in this search by appending them to the $G4LATTICEDATA variable:

export G4LATTICEDATA=${G4LATTICEDATA:+$G4LATTICEDATA:}/path/to/more/CrystalMaps

or

setenv G4LATTICEDATA ${G4LATTICEDATA}:/path/to/more/CrystalMaps

Note that if a material configuration file is found in multiple locations, only the first file found chronologically will be chosen; G4LATTICEDATA must be reset in order for conflicting configuration files to be found. G4CMP is distributed with germanium and silicon configurations, in CrystalMaps/Ge/ and CrystalMaps/Si/, respectively. We recommend naming additional directories by element or material, matching the Geant4 conventions, but this is not required or enforced.

The parameter definition file is config.txt. Each line starts with a keyword, followed by one or more values. Any line which starts with "#" is ignored, as is any text after a "#" on a parameter line. Multiple keywords/value sets may be included on a single line of the file if desired for readability.

Dimensional parameters MUST be specified with the value in each entry. For keywords taking multiple values, a single unit may be specified after the group of values, e.g.,

triclinic 1. 2. 3. Ang 30. 50. 45. deg

where "Ang" and "deg" are the appropriate length and angular dimensions.

The lattice symmetry is specified by one of the seven crystal systems (or "amorphous") followed by the appropriate combination of lattice constant(s) and angle(s) needed to specify it uniquely. The reduced elasticity matrix, Cij, must be specified term by term; which components are needed depends on the crystal system.

Keyword	Arguments	Value type(s)	Units
Lattice parameters
amorphous	-none-	Polycrystalline solid
cubic	a	Lattice constant	length
tetragonal	a c	Lattice constants	length
hexagonal	a c	Lattice constants	length
orthorhombic	a b c	Lattice constants	length
rhombohedral	a alpha	Lattice const., angle	length, deg/rad
monoclinic	a b c alpha	Lattice const., angle	length, deg/rad
triclinic	a b c alpha beta gamma	Lattice const., angle	length, deg/rad
stiffness	i j val	Indices 1-6, elasticity	pressure (Pa, GPa)
Cij	i j val	Indices 1-6, elasticity	Pa, GPa
Phonon parameters
beta	val	scattering parameters	Pa, GPa
gamma	val	(see S. Tamura, PRB 1985)	Pa, GPa
lambda	val		Pa, GPa
mu	val		Pa, GPa
dyn	beta gamma lambda mu	All four params	Pa, GPa
scat	B	isotope scattering rate	second^3 (s3)
decay	A	anharmonic decay rate	second^4 (s4)
decayTT	frac	Fraction of L->TT decays
LDOS	frac	longitudinal density of states	sum to unity
STDOS	frac	slow-transverse density of states
FTDOS	frac	fast-transverse density of states
Debye	val	Debye energy for phonon primaries	E, T, Hz
Charge carrier parameters
vsound	Vlong	sound speed (longitudinal)	m/s
vtrans	Vtrans	sound speed (transverse)	m/s
bandgap	val	Bandgap energy	energy (eV)
pairEnergy	val	Energy taken by e-h pair	energy (eV)
fanoFactor	val	Spread of e-h pair energy
l0_e	len	electron scattering length	length
l0_h	len	hole scattering length	length
hmass	m_h	effective mass of hole	electron mass ratio
emass	m_xx m_yy m_zz	electron mass tensor	(same)
valley	theta phi psi unit	Euler angles	angle (deg/rad)
InterValley scattering with matrix elements
epsilon	e/e0	Relative permittivity
neutDens	N	Number density of neutron impurities	/volume
alpha	val	Non-parabolicity of valleys	energy^-1 (/eV)
acDeform	val	Acoustic deformation potential	energy (eV)
ivDeform	val val ...	Optical deformation potentials	eV/cm
ivEnergy	val val ...	Optical phonon thresholds	energy (eV)
**InterValley scattering (Linear and Quadratic Models) **
ivModel	name	IVRate (matrix), Linear or Quadratic	string
ivLinRate0	val	Constant term in linear IV expression	Hz
ivLinRate1	val	Linear term in linear IV expression	Hz
ivLinPower	exp	Exponent: rate = Rate0 + Rate1* E^exp	none
ivQuadRate	val	Coefficient for quadratic IV expression	Hz
ivQuadField	val	Minimum field for quadratic IV expression	V/m
ivQuadPower	exp	Exponent: rate = Rate*(E^2-Field^2)^(exp/2)	none

Surface Interactions

Transport of both phonons and charge carriers will involve interactions at the surface of a crystal volume. The "boundary processes" are modelled on Geant4's optical physics process, and support reflection, transmission (from one lattice-equipped volume to another), and absorption with configurable probabilities.

User applications should use the G4CMPSurfaceProperty class, or an application-specific subclass. This class has G4MaterialPropertiesTable objects for phonons and charges separately; the base class constructor takes a long list of arguments to fill those tables with common parameters:

G4CMPSurfaceProperty(const G4String& name, G4double qAbsProb, // Prob. to absorb charge carrier G4double qReflProb, // If not absorbed, prob to reflect G4double eMinK, //Min wave number to absorb electron G4double hMinK, //Min wave number to absorb hole G4double pAbsProb, // Prob. to absorb phonon G4double pReflProb, // If not absorbed, prob to reflect G4double pSpecProb, //Prob. of specular reflection G4double pMinK, //Min wave number to absorb phonon G4SurfaceType stype = dielectric_dielectric);

These parameters are sufficient to model absorption or reflection of both charges and phonons at the surface of a crystal. User applications may choose to define both skin surfaces (for bare crystal substrates) and border surfaces (with associated sensor/device volumes attached to the crystal) with different property parameters.

User applications with active sensors for either phonons or charges (or both), should define a subclass of G4CMPVElectrodePattern for each of those sensors. If the sensors require additional parameters, those should be assigned to the material properties table that goes with the surface above. See below for a discussion of G4CMPPhononElectrode.

Phonon sensors typically involve a superconducting film to couple the substrate to a sensor (SQUID, TES, etc.). The G4CMPKaplanQP class provides a parametric model for that coupling, implementing Kaplan's model for energy exchange between phonons and quasiparticles from broken Cooper pairs. This class expects to find the following material properties defined for the metal film (defined using the function G4MaterialPropertyTable::SetConstProperty("key", value);).

Property Key	Definition	Example value (Al)
filmThickness	Thickness of film	600.*nm
gapEnergy	Bandgap of film material	173.715e-6*eV
lowQPLimit	Minimum bandgap multiple for quasiparticles	3.
phononLifetime	Phonon lifetime in film at 2*bandgap	242.*ps
phononLifetimeSlope	Lifetime dependence vs. energy	0.29
vSound	Speed of sound in film	3.26*km/s
lowQPLimit	Minimum QP energy to radiate phonons	3.
highQPLimit	Maximum energy to create QPs	10.
subgapAbsorption	Probability to absorb energy below 2*bandgap	0.03 (optional)
absorberGap	Bandgap of "subgap absorber"	15e-6*eV (tungsten)
absorberEff	Quasiparticle absorption efficiency	0.3
absorberEffSlope	Efficiency dependence vs. energy	0.
temperature	Temperature of film	0.05e-3*K

The last five parameters are optional. They only apply if there is a sensor involved which is sensitive to heat energy, in which case phonons below 2.*bandgap energy, and above 2.*absorberGap energy, should be treated as directly absorbed with the specified 'subgapAbsorption'. In this case, we recommend that user applications also set /g4cmp/minEPhonons to 2.*absorberGap, to avoid excessive CPU from tracking unmeasurable phonons. Quasiparticles in a sensor may be subject to a baseline absorption efficiency 'absorberEff' and energy-dependent efficiency modification 'absorberEffSlope'.

The G4CMPKaplanQP process also respects the global setting kaplanKeepPhonons. If this is set true, then all internal phonons produced in the film will be either re-emitted into the substrate, or iterated to produce multiple quasiparticles for energy collection.

A concrete "electrode" class, G4CMPPhononElectrode, is provided for simple access to G4CMPKaplanQP from user applications. An instance of G4CMPPhononElectrode should be registered to the G4CMPSurfaceProperty associated with the phonon sensors' surface. The material properties listed above should be registered into the surface's material property table, via G4CMPSurfaceProperty::GetPhononMaterialPropertiesTablePointer(); this table will be passed into G4CMPKaplanQP automatically when it is registered.

G4CMPPhononElectrode also supports an additional material property, "filmAbsorption", to specify the "conversion efficiency" for phonons incident on the registered sensor. This assumes that the sensor is implemented as a dedicated volume with an associated border surface. If individual sensor shapes are not implemented, this parameter may also include geometric coverage.