Exemplary methods of forming a semiconductor structure may include forming a doped silicon layer on a semiconductor substrate. A level of doping may be increased at an increasing distance from the semiconductor substrate. The methods may include etching the doped silicon layer to define a trench extending to the semiconductor substrate. The doped silicon layer may define a sloping sidewall of the trench. The trench may be characterized by a depth of greater than or about 30 μm. The methods may include lining the trench with a first oxide material. The methods may include depositing a second oxide material within the trench. The methods may include forming a contact to produce a power device.