Abnormal transition from unconventional field emission to space charge limited current

The transition from source limited electron emission like field emission at low voltage to bulk transport limited by space charge effects at high voltage is widely accepted. In this paper, we report that this understanding is no longer valid if the field emission is not strictly obeying the scaling based on the Fowler-Nordheim (FN) law. By using a generalized field emission model in the form of ln(J/F k ) vs -1/F, where J is the current density, F is the applied field, and k is arbitrary value, we show that there are 3 different operating regimes, which depends on k (with respect to a critical value k c ≡ 3/2) and also the gap spacing D: 1. Super-critical regime at k > k c , we have 2-state transition from FE to SCLC at all D. This is similar to the traditional understanding for FN law (at k = 2). 2. Critical regime at k = k c , we have exclusive (or pure FE) with absolute absence of SCLC at small D and 2-stage transition from FE to SCLC at larger D. 3. Sub-critical regime at k < k c , we have exclusive (or pure FE) with absolute absence of SCLC at small D and 3-state transition from FE to SCLC at larger D.