Analysis of minority carrier lifetime for InAlAs/InGaAs high electron mobility transistors by using 1.55-μm femto-second pulse laser

The minority carrier lifetime (τ) of High electron mobility transistors (HEMTs) made using the InAlAs/InGaAs material system lattice-matched to the InP substrate had been obtained from optical response measurements with a 1.55-μm femto-second pulse laser where the laser was illuminated onto the backside of a wafer. The drain current of HEMTs associated with the optical pulse was detected using a digitizing oscilloscope, and τ was estimated from the exponential dependence of drain current on time. In our current investigation, we found that τ is dominated by the following modes: (1) the amount of time required for holes to transit across the channel toward the source, and (2) the amount of time required for the holes accumulated in the source region to recombine with two-dimensional electron gas (2DEG) through the Auger mechanism. Because the sheet concentration (p_s) of holes accumulated in source region is low at a low source-to-drain voltage (V _DS), Auger recombination is not predominant, and τ was only dominated by the hole transit time. At a high V_DS, p_s became high enough for Auger recombination to occur and dominate τ. Furthermore, we investigated the optical power dependence of τ where the optical power was supplied in a continuous wave (CW) to generate photo-excited holes in a steady state. The value of τ decreased monotonically as V _DS increased and saturated in as little as 6x10^-10 s when the optical power was increased. The theoretical investigation was made to understand this saturation phenomenon.