The above expression results in n ~ 7.5, which gives us k ~ 3.6 nm from equation (2). This indicates that the dopant concentration, with depth, varies hyperbolically as ~ 1/z 7.5 and the holographic phase shift as ~ 1/z 4.5 . In equation ( ), the polynomial terms are a result of integration constants, which signify the presence of static charge, electric field, voltage, etc. All these combined result in MIP of the stack. The exact origins of the MIP can be numerous such as electron density variation, traps, defects, impurities and other lattice imperfections . Furthermore, it is also known that increasing donor atoms (higher electron concentration) results in higher MIP and increased acceptor atoms (higher hole concentration) results in lower MIP . This matches the expected trend seen in fig , which shows increased mean phase shift with higher Phosphorus doping. Some signs of polynomial term dependence can be seen in such as On the other hand, the holographic phase range varies as Recipe 1 > Recipe 3 > Recipe 2. This is unexpected since holographic phase range is expected to trend closely with doping. A higher substitutional doping should lead to increased built-in voltage and hence higher holographic phase range, which doesn't match with the observed trend. This indicates that as we go from Recipe 1 → Recipe 2, we do increase the overall substitutional P concentration, but some of the carriers from these dopants haven't contributed to the dynamic built-in voltage (hyperbolic term in equation ) and have instead contributed to MIP (Polynomial terms in equation 8), further indicating the effects of trapped states at the interface between epitaxial Si:P and substrate. As we go from recipe 2 → recipe 3, we do increase the overall phase mean and range. This indicates that some of the increased substitutional dopants have resulted in increased dynamic voltage, and some have contributed to MIP. This leads to positively charged donor atoms in the Si:P layer and some negatively charged acceptor atoms inside the substrate, creating a built-in voltage, such that the diffusion of carriers reaches an equilibrium. As we increase the doping, we see an increased diffusion due to larger difference in carrier concentration across the interface. This should lead to a higher built-in voltage, which shows as an increased range in holographic phase difference. However, higher P concentration also leads to increased trap states (indicated by grey balls), which leads to static charge, thereby contributing to higher MIP. As we increase the doping even further (Recipe 3), the trap states start to dominate which lead to increased holographic mean phase. As these trap states dominate, the overall dynamic charge decreases. This decrease in dynamic charge leads to decreased holographic phase range. This is further complicated by the fact that the interface characteristics are heavily dependent on the interface defects. Increasing the overall doping, results in a higher lattice strain (Fig ), which can increase the overall defect density and dislocations.