I wanted to study the effect of temperature change on diode characteristics. I used a 1N4739A 9.1 V Zener diode for that and connected it in reverse bias. Since the meter is not that sensitive to measure leakage current, I increased the voltage above 9 volt to breakdown region. Introducing a heat source to the vicinity of the diode, the current starts decreasing. How do we explain that behaviour? The diode resistance is supposed to decrease with increase in temperature right?