PN Junction model from Sze

CHANGELOG.md

@@ -1,5 +1,15 @@
 # Changelog
 
+## Unreleased
+
+- PN-junction depletion model from Sze *Physics of Semiconductor Devices* (`PNJunctionConfig`,
+  `make_pn_junction_profile`): computes built-in voltage, depletion width `W` (abrupt or linearly graded), asymmetric
+  P/N split `x_p`/`x_n`, and capacitance `C_j = eps_s A / W`. The depletion region is represented automatically — meshed
+  as a dielectric strip in high-res mode when `W >= ~1/5` of the flanking doped sections, otherwise applied as a lumped
+  Impedance boundary via `sim.set_pn_junction()`. The 2D TWMZM demo now illustrates both modes.
+- Fix: `build_doped_cross_section()` now registers doping/rib materials on `stack.materials`; previously doped domains
+  silently resolved to eps=1.0 without conductivity in generated Palace configs.
+
 ## 0.1.0
 
 - Electrostatic simulation end-to-end for Palace ([#146](https://github.com/gdsfactory/gsim/pull/146))

README.md

@@ -32,11 +32,9 @@ with minimal boilerplate.
 pip install gsim
 ```
 
-For local Palace execution on Linux x86_64, install the optional prebuilt binary separately:
-
-```bash
-pip install "palacetoolkit-palace-cpu @ https://github.com/EpsilonForge/PalaceToolkit/releases/download/palace-cpu-v0.1.2/palacetoolkit_palace_cpu-0.1.0-py3-none-linux_x86_64.whl"
-```
+For local Palace execution on Linux x86_64, gsim can auto-download and cache a prebuilt Palace CPU binary on first use.
+No additional package installation is required. If you prefer to supply a binary yourself, set `PALACE_BIN` (path to an
+executable) or put `palace` on your `PATH`; a Palace SIF image may be given via `PALACE_SIF` for Apptainer-based runs.
 
 For development (requires [uv](https://docs.astral.sh/uv/)):
 

docs/api/common.md

@@ -38,6 +38,38 @@
       inherited_members: false
       members: false
 
+## PN Junction
+
+Depletion model after Sze & Ng, *Physics of Semiconductor Devices*, ch. 2.
+
+::: gsim.common.stack.PNJunctionConfig
+    options:
+      show_source: false
+
+::: gsim.common.stack.make_pn_junction_profile
+    options:
+      show_source: false
+
+::: gsim.common.stack.built_in_voltage
+    options:
+      show_source: false
+
+::: gsim.common.stack.depletion_width
+    options:
+      show_source: false
+
+::: gsim.common.stack.depletion_extents
+    options:
+      show_source: false
+
+::: gsim.common.stack.junction_capacitance_per_area
+    options:
+      show_source: false
+
+::: gsim.common.stack.select_junction_mode
+    options:
+      show_source: false
+
 ## Visualization
 
 ::: gsim.common.viz.plot_prisms_3d