Turnover phenomenon in N ? N Si devices and second breakdown in transistors

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Abstract
Turnover phenomenon in N νl N Si devices was studied in relation to second breakdown in NP ν N Si transistors. The devices were fabricated by a usual diffusion method using P2O5powder as diffusant source. Four groups of the devices, each having a diameter of 1.0 mm, a thickness of 0.25 mm, a resistivity in ν layer ranging from 3 to 210 ohm-cm, and a surface concentration in N layer of 2 × 1020cm-3, were tested under two kinds of applied voltage. The applied voltage was a half-cycle voltage from ac source and single-pulse voltage with a rising and flat part. The field strength in ν layer was below 3 × 103v/cm. The voltage vs. current characteristics and the transient figures of voltage and current were observed on a memoriscope, and the temperature of the device was determined using temperature sensitive paints. The current increases linearly with the increasing voltage at the onset of the V-I curve, and saturates with further increases in voltage. Turnover occurs after the large departure from ohmic behavior in V-I characteristics. At the turnover, the temperature of the device was estimated to be near intrinsic; 160°C for the device with ∼ 210 ohm-cm, 330°C for ∼ 3 ohm-cm. The discussions on turnover characteristics are made in terms of the decrease in carrier mobility, the increase in carrier concentration in ν layer, and the current constriction in the device.