In this study, we demonstrate an approach to identify defects in wide band gap semiconductors by comparing accumulatively-recorded derivative steady-state photo-capacitance (SSPC) spectra to simulations using results from first-principles calculations. Specifically, we present a method to simulate SSPC spectra which adopts inputs both from first-principles calculations and the experimental conditions. The applicability of the developed method is demonstrated using the cases of subsitutional Fe (FeGa) and Ti (TiGa) defects in β-Ga2O3. Using deep-level transient spectroscopy, we identify defect levels associated with
Fe
GaI
0
/
−
(E
A = 0.66 eV),
Fe
GaII
0
/
−
(E
A = 0.79 eV) and
Ti
GaII
+
/
0
(E
A = 1.03 eV) in the β-Ga2O3 samples studied here. Accumulatively-recorded SSPC spectra reveal several defect levels labeled
T
1
E
F
G
–
T
6
E
F
G
with onsets for optical absorption between 1.5 eV and 4.3 eV. The signature
T
1
E
F
G
consists of several overlapping defect signatures, and is identified as being related to
Fe
GaI
0
/
−
,
Fe
GaII
0
/
−
and
Ti
GaII
+
/
0
by comparing measured and simulated accumulatively-recorded derivative SSPC spectra.