  We re-analyzed the Herschel/PACS data of a sample of 55 brown dwarfs (BDs)
and very low mass stars with spectral types ranging from M5.5 to L0. We
investigated the dependence of disk structure on the mass of the central object
in the substellar regime based on a homogeneous analysis of Herschel data from
flux density measurements to spectral energy distribution (SED) modeling. A
systematic comparison between the derived disk properties and those of sun-like
stars shows that the disk flaring of BDs and very low mass stars is generally
smaller than that of their higher mass counterparts, the disk mass is orders of
magnitude lower than the typical value found in T Tauri stars, and the disk
scale heights are comparable in both sun-like stars and BDs. We further divided
our sample into an early-type brown dwarf (ETBD) group and a late-type brown
dwarf (LTBD) group by using spectral type (=M8) as the border criterion. We
systematically compared the modeling results from Bayesian analysis between
these two groups, and found the trends of flaring index as a function of
spectral type also present in the substellar regime. The spectral type
independence of the scale height is also seen between high-mass and very
low-mass BDs. However, both the ETBD and LTBD groups feature a similar median
disk mass of 10^{-5}Msun and no clear trend is visible in the distribution,
probably due to the uncertainty in translating the far-IR photometry into disk
mass, the detection bias and the age difference among the sample. Unlike
previous studies, our analysis is completely homogeneous in Herschel/PACS data
reduction and modeling with a statistically significant sample. Therefore, we
present evidence of stellar-mass-dependent disk structure down to the
substellar mass regime, which is important for planet formation models.
(Abridged Version)
