The below-bandgap photoluminescence (PL) from semi-insulating (s.i.) GaAs is investigated. It is found that various electronic states that give rise to nearinfrared (NIR) PL peaks are generated through processes that are standard for epitaxial growth of InAlGaAs structures on (001) GaAs substrates. Moreover, the PL signals from these states overlap with those from InAs quantum dots, wetting layers, and InGaAs structures, complicating the design of devices for telecommunications or intermediate band solar cells. The spatial positions of the various defects are also investigated by below-gap excitation and back-illuminated PL measurements. The possible identities of the defects are also presented. The present results provide guidelines for distinguishing the desired electronic states from thermal treatment-induced defect states.

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We report the observation of below-GaAs-bandgap photoluminescence (PL) emission from semi-insulating GaAs substrates subjected to thermal annealing during the standard pre-MBE-growth processes. The below-GaAs-bandgap luminescence from defects were investigated using a combination of PL techniques including below-gap-excitation (BGE) and backside illuminated (BI) PL. Using BGE and BI PL, defects deep within the substrates were probed, and their spatial positions along the sample were analyzed. A PL peak at 1000 nm was observed after pre-bake annealing at 300°C, and further peaks at 905, 940 and 1150 nm were found after oxide desorption annealing at 600°C. These are attributed to the Ga-vacancy related defect, Ga-vacancy-complex defect, As-vacancy defect, and InGaAs states, respectively. This is the first report of the formation of such optically-active defects after annealing of GaAs at moderate temperature ranges (≤600°C), providing guidelines to distinguish desired electronic states for device applications from those that arise from defects which often confuse, and also degrade the device performances.

The below‐bandgap photoluminescence (PL) from semi‐insulating (s.i.) GaAs is investigated. It is found that various electronic states that give rise to near‐infrared (NIR) PL peaks are generated through processes that are standard for epitaxial growth of InAlGaAs structures on (001) GaAs substrates. Moreover, the PL signals from these states overlap with those from InAs quantum dots, wetting layers, and InGaAs structures, complicating the design of devices for telecommunications or intermediate band solar cells. The spatial positions of the various defects are also investigated by below‐gap excitation and back‐illuminated PL measurements. The possible identities of the defects are also presented. The present results provide guidelines for distinguishing the desired electronic states from thermal treatment‐induced defect states.

Below-bandgap states induced by pre-epitaxial growth treatments in semi-insulating (s.i.) GaAs has previously been investigated by photoluminescence (PL). Various electronic states giving rise to near-infrared PL peaks are generated through processes such as annealing or buffer growth that are standard for epitaxial growth of InAlGaAs structures on (001) GaAs substrates. These states often overlap with those from InGaAs structures, not only complicating the interpretation but also altering the electronic properties of the devices. The present study extends the investigation to the case of doped n-and p-type (001) GaAs substrates. These substrates are widely utilized in various optoelectronic applications, and therefore information on below bandgap states are important to distinguish the desired electronic states from the pre-growth treatment-induced defect states. It was found that the behavior of n-and p-type substrates subjected to pre-growth treatment are different from that of s.i. GaAs.