DADOS uses these kinds of defects for simulations (please click on them for more information):

• Amorphous.
• AmorphousPockets.
• Complex.
• DLoops.
• I311.
• Platelet.
• PointD.
• SiInterface.
• SuperSat.
• Voids.

Amorphous, SiInterface are not exactly defects, but they have associated events (read below).

SuperSat is not a defect but are included here for an easier handling and visualization.

DADOS distinguishes between events and interactions for simulating:

• Events happen by themselves, with a frequency that depends on the temperature. For example: point defects jumps.

• Interactions are related with capture distance. As we will see later, the only mobile defects implemented in DADOS are point defects, and therefore the interactions are going to take place between (mobile) point defects and any other defect. For example: cluster growth. Interactions occur in DADOS depending on:
  • Whether or not the interaction is allowed,
  • Involved barrier energies,
  • Charge states.

To clarify ideas, emissions are always events whereas captures are always interactions.

Particles in DADOS are always associated to defects, which are the ones used to create events.

The events are shown in the messages window, as we can see in the figure below. These events are basically associated to jumps, because these are the most frequent ones.

All implemented defects are neutral except, in some cases, point defects.

Amorphous

Description

Amorphous silicon [1].

Particles involved

None [2, 3, 4].

Events allowed

• Recrystallization.

Interactions allowed

None.

Related DADOS mechanisms

• Amorphous implementation.

• Trapping.

Comments

1. It is important to make the difference between amorphous as a defect and amorphous box:
   • Amorphous silicon is not crystalline with a lot of defects. It is a different material, although DADOS implements it as crystalline silicon with a concentration of native defects that has reached a certain threshold.
   • Amorphous silicon is a defect for DADOS as events occur there and in order to view concentrations: The program provides with a concentration for amorphous boxes (but they are not real particles).

2. When a dopant is in an amorphous box, it is not considered to belong to the amorphous defect but is considered to be a new point defect to whose name is added "AmorphousSi", e.g. "BAmorphousSi". We call this "impurities in other materials".
3. Both interstitials and vacancies are used for visualization, but they are not actually amorphous particles. Amorphous boxes contribute to the interstitials and vacancies profiles with concentration values similar to the amorphization threshold.
4. Internally, DADOS keeps the balance of I-V particles.

 

AmorphousPockets

Description

Amorphous pocket: Initial damage structure, with interstitials and/or vacancies in an irregular shape.

Particles involved

Single neutral native defects [1].

Events allowed

• IV recombination, i.e. shrinkage [2].

• Neutral interstitials emission [4, 5].

• Neutral vacancies emission [4, 6].

Interactions allowed

• I capture [5], but only if:

  • Captured I is neutral OR,

  • Captured I is charged but the amorphous pocket contains one or more vacancies.
     

• V capture [6], but only if:

  • Captured V is neutral OR,

  • Captured V is charged but the amorphous pocket contains one or more interstitials.
     

• Bi capture [7] but only if:

  • Amorphous pocket contains one or more interstitials and one or more vacancies.

Related DADOS mechanisms

• Amorphization.
• Amorphous pocket implementation.
• Amorphous pocket to I311 transformation.
• Amorphous pocket to void transformation.

Comments

1. Small and irregularly shaped I clusters or V clusters are regarded as a particular case of amorphous pockets with only one type of particles.
2. Amorphous pockets can shrink due to emissions and recombinations. However, although both effects are implemented in DADOS, the latter is more important, as its frequency is much higher.
3. Particles in amorphous pockets are immobile.
4. Obviously, emission of interstitials or vacancies is allowed only if there are any.
5. Let's suppose some cases:

   I_m + I <-> I_m+1

   This reaction is allowed in both directions as DADOS implements both emission and capture of neutral particles. However, it is allowed neither the emission nor capture of charged particles. If this phenomena were implemented, then emission frequency would depend on Fermi level. What DADOS does is to maintain this rate constant and include the charges effects in charge update handling.

   I_mV_n + I <-> I_m+1V_n,    m≥0, n>0

   The reaction above is allowed in both directions but the the reverse one (<-) is not frequent due to the shrinkage occurs before more likely.

   I_mV_n + I^j -> I_m+1V_n + j

   "j" is an integer that represents the charge and jh⁺ (or je^-) are the holes (or electrons) required to balance the charge reaction. This reaction is only allowed in the forward direction. In DADOS, it is not allowed the emission of charged particles. If this phenomenon was implemented, then emission frequency would depend on Fermi level. What DADOS does is to maintain this rate constant and the charges effects are included in charge update handling.

6. Let's suppose some cases:

   V_m + V <-> V_m+1

   This reaction is allowed in both directions as DADOS implements both emission and capture of neutral particles. However, it is allowed neither the emission nor capture of charged particles. If this phenomena were implemented, then emission frequency would depend on Fermi level. What DADOS does is to maintain this rate constant and include the charges effects in charge update handling.

   I_mV_n + V <-> I_mV_n+1,    n≥0, m>0

   The reaction above is allowed in both directions but the the reverse one (<-) is not frequent due to the shrinkage occurs before more likely.

   I_mV_n + V^j -> I_mV_n+1 + jh⁺

   "j" is an integer that represents the charge and jh⁺ (or je^-) are the holes (or electrons) required to balance the charge reaction. . This reaction is only allowed in the forward direction. In DADOS, it is not allowed the emission of charged particles. If this phenomenon was implemented, then emission frequency would depend on Fermi level. What DADOS does is to maintain this rate constant and the charges effects are included in charge update handling.

7. In order to simulate the immobilization of Bis by amorphous pockets, we assume the following reaction:

   Bi + I_mV_n -> I₂B + I_m-1V_n

   We assume that the interaction of Bis with an amorphous pocket with only one type of particle (I_m or V_n) is not allowed because there is no evidence that boron activation in vacancies clusters or boron pile-up in interstitials clusters is observed experimentally.

8. With reasonable values of binding energy (Eb), the rate of the mechanism V_n -> V_n+1 + I or I_n -> I_n+1 + V is negligible. Therefore, this event is not implemented. WARNING: If binding energy is higher (or much higher) than formation energy, the simulation can give inaccurate results as the suppositions are not true.
9. The trasformation from an amorphous pocket with only one type of particle to either a I311 or a void is a particular type of event, depending on the temperature.
10. Amorphous pockets accumulation generates amorphous regions.
11. Amorphous pockets are considered to be electrically neutral.

 

Complex

Description

Complex, i.e., structures of impurities (dopants) and interstitials or vacancies.

Implemented types: I_mB_n, I_mC_n, V_mAs_n, V_mO_n, V_mF_n, V_mPh_n. "n" and "m" are the number of particles of each type. "m" can be zero, therefore impurities clusters are included here.

Particles involved

Two types of particles:

• "Back particles": Single neutral "native defects".

• "Front particles": Single impurities.

Events allowed [1]

• Back particle emission: emits a back particle.

• Front particle emission:

  • Mobile particles are emitted as single particles (e.g. fluorine).

  F_nV_m -> V_mF_n-1 + F

  • Immobile particles are emitted as a pair, for example:

  B_nI_m -> B_n-1I_m-1 + Bi
  As_nV_m -> As_n-1V_m-1 + AsV
   

• Complementary particle emission (e.g. V_mAs_n -> V_m+1As_n + I). This event is a generalization of Frank-Turnbull mechanism. [2].

Interactions allowed

• Neutral point defect capture,

  • with growth (e.g. V_nAs_m + V -> V_nAs_m+1) or,
  • with recombination (e.g. V_nAs_m + Asi -> V_n-1As_m+1) [3].
     

• Complex capture (e.g. V_nAs_m + AsV -> V_n+1As_m+1).

Related DADOS mechanisms

• Complex implementation.
• Pile-up.

Comments

1. Emitted particles are neutral and, consequently, the reverse processes of these (interactions) are only allowed with neutral point defects, in order to maintain microscopic reversibility.
2. Complementary particle emission is implemented here and not in amorphous pockets because in complexes it is much more frequent. Notice that in some particular cases, due to the complexes energies, this process could be frequent; therefore, in this case, it would not be consistent to allow recombination with charged native point defects.
(Pinacho et al. 2005)
3. Recombination is immediate as, in DADOS, activation energy for complex shrinkage is assumed to be zero.
4. Complexes are considered to be neutral and they are responsible for electrical deactivation of some dopants (such as boron or arsenic) (Pelaz et al. 1997).
5. Complexes dissolution implies an electrical reactivation (Pelaz et al. 1999).
6. Particles in complexes are immobile.

DLoops

Description

Faulted dislocation loop [1]: Planar extended defect of interstitials in {111} orientations.

Particles involved

Neutral interstitials.

Events allowed

• Neutral interstitials emission [2].

Interactions allowed [3]

• Captures of:

  • Neutral interstitials.
  • Interstitial boron.

Related DADOS mechanisms

• Dislocation loop implementation.
• I311 to dislocation loop transformation.
• Pile-up.

Comments

1. Perfect dislocation loops are not implemented in the current version of DADOS (Cristiano et al. 2000).
2. Neutral vacancies emission and captures are not implemented yet. [TO BE DEVELOPED]
3. Interactions for dislocation loops are the reverse process of neutral interstitials emission.
4. Particles in dislocation loops are immobile.
5. In the current version of DADOS, dislocation loops in DADOS are formed from I311.
    

I311

Description

Extended defect of neutral interstitials in {311} orientations.

Particles involved

Neutral interstitials.

Events allowed

• Neutral interstitials emission.

• Transformation into a dislocation loop (large I311s).

Interactions allowed

• Neutral interstitials capture (growth).

• V capture and recombination [2].

• Capture of some types of dopants, although only indium is implemented [3].

Related DADOS mechanisms

• Amorphous pockets to I311 transformation.
• I311 implementation.
• I311 to dislocation loops transformation.
• Pile-up.

Comments

1. Particles in I311 clusters are immobile.
2. Recombination is immediate, as in DADOS, activation energy for shrinkage is assumed to be zero. Captures and recombination with charged vacancies is allowed as vacancies emission from I_m structures is going to be very unlikely.
3. When a mobile Indium-vacancy or Indium-interstitial pair meets a 311 cluster, the Indium atom piles up:

   Ini(-) + I_m -> In(-) + I_m+1
   InV(-) + I_m -> In(-) + I_m-1

   This way, the indium atom maintains the negative charge.

4. I311 are normally created from amorphous pockets with only interstitials at enough temperature.

 

Platelet [TO BE DEVELOPED]

Description

Platelet: Extended defect in {100} orientations.

Particles involved

Neutral vacancies and hydrogen.

Comments

1. Particles in platelets are immobile.
2. This defect is under development.

PointD

Description

Native point defects: They are formed by one particle (either single neutral "native defects", charged "native defects", single impurities or impurity-"native defect" pairs).

They can be:

• Native defects, such as interstitials, vacancies, neutral (I, V) or charged (IP, IM, VM, VMM, VP, VPP).
• Substitutional dopants pairs, such as Bi (boron + interstitial), AsV (arsenic + vacancy), etc. [1]

Particles involved

Any particle.

Events allowed

• Migration [1].

• Break-up (for pairs only):

  • Releasing an interstitial (e.g. Asi -> As + IM).

  • Releasing a vacancy (e.g. AsV -> As + VM).

Interactions allowed

• Interactions among point defects are set in the DDP file, section PointD Interactions. PointD Interactions are set to be false by default. To enable one interaction please use the keyword "EnableInteraction" and then write the two species to interact, the result of the interaction (AmPock, PointD or ImpCluster) and the type of ImpCluster (I or V) or the resulting point defect (none for AmPock). For instance, if we want to enable the interaction between boron and interstitial to create an interstitial boron, we should add to DDP file:

  EnableInteraction I B     PointD Bi

  Please, see [2, 3, 4, 5, 6, 7] for further information.

• Interactions with other defects are explained in the corresponding sections of those defects.

Related DADOS mechanisms

• Charge update.

• Point defect implementation.

Comments

1. All mobile particles are point defects, but not all point defects are mobile. All defects are implemented in the same way, and for those which are immobile, the prefactor of migration is set to zero.
2. Break-up reactions implemented in DADOS are those that keep the total charge (Martin-Bragado et al. 2005). For instance, AsV (neutral) would break up as As + VM (because the charges or As and VM are +1 and -1 respectively).

3. Break-up mechanism can not be currently cancelled using the EnableInteraction keyword [4] in the DDP file.
4. It is not recommended to allow an interaction that would be the reverse process of a break-up reactions in which the charge would not be (and that, in consequence, is not implemented [3]) kept. For instance,

   EnableInteraction IP C        PointD Ci

   Because CiP, the hypothetical result, is not implemented, and problems of microscopic reversibility would appear.

5. Interactions among point defects that eventually would lead to recombination can be allowed with no noticeable problems of microscopic reversability because their reverse reactions (involving generation) would be in any case very infrequent.

6. In the EnableInteraction sentence, we do not specify the charge in the resulting point defect because DADOS handles it. For instance: EnableInteraction I B PointD Bi, will give as a result BiM, or EnableInteraction I AsVM PointD As will give as a results AsP because in the recombination process it is not necessary to keep the charge.
7. It is not allowed the interaction of particles of the same charge sign in order to assess short range coulombic repulsions.
Long range coulombic attractions and repulsions in DADOS, are implemented by means of the electric drift (Martin-Bragado et al. 2005).

 

SiInterface

Description

Silicon interface: Two materials are needed here. One of them must be silicon and the other can be silicon oxide, silicon nitride or ambient [2] (these are the ones currently implemented in DADOS).

Particles involved

SiInterface is not formed by particles, but it counts the number of single impurities trapped on it (see trapping).

Events allowed [1,3]

• Single neutral native defects emission. [5,6]

• Dopants emission: AsV, Asi, Bi, Ci, F, Phi, PhV.

Interactions allowed [3]

• Captures of: mobile neutral point defects: I, V, AsV, Asi, Bi, Ci, F, Phi, PhV.

Related DADOS mechanisms

• Interface implementation.

• Segregation.

• Trapping.

Related physical magnitudes

• Recombination length. [4]
• Solubility.

Comments

1. Events are the reverse processes of captures.
2. Silicon-amorphous is not managed as an interface because it neither traps nor emit interstitials or vacancies (at least not in the same way as others).
3. Both interactions and events are only implemented with neutral particles.
4. The probability of capture of interstitials and vacancies is controlled by the recombination length, defined in the DDP file by the parameter RecLnm.
5. The emission rate for interstitials and vacancies can be set different from the equilibrium one by using the command SuperSat.
6. No interfaces are considered in the border between silicon and silicon-germanium or silicon-germanium and silicon-germanium (alloys) because they neither trap nor emit interstitials or vacancies (at least not in the same way as others). [TO BE DEVELOPED]

SuperSat

See Supersaturation.

Comments

1. Supersaturation is included here to help visualization. After choosing the particle (interstitials or vacancies), you are allowed to choose the SuperSat option in defects.

 

Voids

Description

Voids: Rounded extended defects of neutral vacancies.

Particles involved

Neutral vacancies.

Events allowed

• Neutral vacancy emission [3].

Interactions allowed

• Neutral vacancy capture (growth).

• Interstitial capture and recombination [1].

Related DADOS mechanisms

• Amorphous pocket to void transformation.
• Void implementation.

Comments

1. Recombination is immediate, as in DADOS, activation energy for void shinkage is assumed to be zero.
2. Particles in voids are immobile.
3. Neutral interstitial emission will be developed.